The PYTHON_MAJOR_MINOR build arg has been deprecated (#15054)

The python version is now auto-detected and the former
build-arg is deprecated.

Time to remove it.

IMAGES.rst

@@ -450,7 +450,6 @@ additional apt dev and runtime dependencies.
 
   docker build . -f Dockerfile.ci \
     --build-arg PYTHON_BASE_IMAGE="python:3.7-slim-buster" \
-    --build-arg PYTHON_MAJOR_MINOR_VERSION=3.7 \
     --build-arg AIRFLOW_INSTALLATION_METHOD="apache-airflow" \
     --build-arg AIRFLOW_VERSION="2.0.0" \
     --build-arg AIRFLOW_VERSION_SPECIFICATION="==2.0.0" \
@@ -484,7 +483,6 @@ based on example in `this comment </~https://github.com/apache/airflow/issues/8605
 
   docker build . -f Dockerfile.ci \
     --build-arg PYTHON_BASE_IMAGE="python:3.7-slim-buster" \
-    --build-arg PYTHON_MAJOR_MINOR_VERSION=3.7 \
     --build-arg AIRFLOW_INSTALLATION_METHOD="apache-airflow" \
     --build-arg AIRFLOW_VERSION="2.0.0" \
     --build-arg AIRFLOW_VERSION_SPECIFICATION="==2.0.0" \
@@ -684,45 +682,44 @@ This builds the CI image in version 3.7 with default extras ("all").
 
 .. code-block:: bash
 
-  docker build . -f Dockerfile.ci --build-arg PYTHON_BASE_IMAGE="python:3.7-slim-buster" \
-    --build-arg PYTHON_MAJOR_MINOR_VERSION=3.7
+  docker build . -f Dockerfile.ci --build-arg PYTHON_BASE_IMAGE="python:3.7-slim-buster"
 
 
 This builds the CI image in version 3.6 with "gcp" extra only.
 
 .. code-block:: bash
 
   docker build . -f Dockerfile.ci --build-arg PYTHON_BASE_IMAGE="python:3.7-slim-buster" \
-    --build-arg PYTHON_MAJOR_MINOR_VERSION=3.6 --build-arg AIRFLOW_EXTRAS=gcp
+    --build-arg AIRFLOW_EXTRAS=gcp
 
 
 This builds the CI image in version 3.6 with "apache-beam" extra added.
 
 .. code-block:: bash
 
   docker build . -f Dockerfile.ci --build-arg PYTHON_BASE_IMAGE="python:3.7-slim-buster" \
-    --build-arg PYTHON_MAJOR_MINOR_VERSION=3.6 --build-arg ADDITIONAL_AIRFLOW_EXTRAS="apache-beam"
+    --build-arg ADDITIONAL_AIRFLOW_EXTRAS="apache-beam"
 
 This builds the CI image in version 3.6 with "mssql" additional package added.
 
 .. code-block:: bash
 
   docker build . -f Dockerfile.ci --build-arg PYTHON_BASE_IMAGE="python:3.7-slim-buster" \
-    --build-arg PYTHON_MAJOR_MINOR_VERSION=3.6 --build-arg ADDITIONAL_PYTHON_DEPS="mssql"
+    --build-arg ADDITIONAL_PYTHON_DEPS="mssql"
 
 This builds the CI image in version 3.6 with "gcc" and "g++" additional apt dev dependencies added.
 
 .. code-block::
 
   docker build . -f Dockerfile.ci --build-arg PYTHON_BASE_IMAGE="python:3.7-slim-buster" \
-    --build-arg PYTHON_MAJOR_MINOR_VERSION=3.6 --build-arg ADDITIONAL_DEV_APT_DEPS="gcc g++"
+    --build-arg ADDITIONAL_DEV_APT_DEPS="gcc g++"
 
 This builds the CI image in version 3.6 with "jdbc" extra and "default-jre-headless" additional apt runtime dependencies added.
 
 .. code-block::
 
   docker build . -f Dockerfile.ci --build-arg PYTHON_BASE_IMAGE="python:3.7-slim-buster" \
-    --build-arg PYTHON_MAJOR_MINOR_VERSION=3.6 --build-arg AIRFLOW_EXTRAS=jdbc --build-arg ADDITIONAL_RUNTIME_DEPS="default-jre-headless"
+    --build-arg AIRFLOW_EXTRAS=jdbc --build-arg ADDITIONAL_RUNTIME_DEPS="default-jre-headless"
 
 Production images
 -----------------

scripts/ci/libraries/_build_images.sh

@@ -748,7 +748,6 @@ Docker building ${AIRFLOW_CI_IMAGE}.
     docker build \
         "${EXTRA_DOCKER_CI_BUILD_FLAGS[@]}" \
         --build-arg PYTHON_BASE_IMAGE="${AIRFLOW_PYTHON_BASE_IMAGE}" \
-        --build-arg PYTHON_MAJOR_MINOR_VERSION="${PYTHON_MAJOR_MINOR_VERSION}" \
         --build-arg AIRFLOW_VERSION="${AIRFLOW_VERSION}" \
         --build-arg AIRFLOW_BRANCH="${BRANCH_NAME}" \
         --build-arg AIRFLOW_EXTRAS="${AIRFLOW_EXTRAS}" \
@@ -902,7 +901,6 @@ function build_images::build_prod_images() {
     docker build \
         "${EXTRA_DOCKER_PROD_BUILD_FLAGS[@]}" \
         --build-arg PYTHON_BASE_IMAGE="${AIRFLOW_PYTHON_BASE_IMAGE}" \
-        --build-arg PYTHON_MAJOR_MINOR_VERSION="${PYTHON_MAJOR_MINOR_VERSION}" \
         --build-arg INSTALL_MYSQL_CLIENT="${INSTALL_MYSQL_CLIENT}" \
         --build-arg AIRFLOW_VERSION="${AIRFLOW_VERSION}" \
         --build-arg AIRFLOW_BRANCH="${AIRFLOW_BRANCH_FOR_PYPI_PRELOADING}" \
@@ -939,7 +937,6 @@ function build_images::build_prod_images() {
     docker build \
         "${EXTRA_DOCKER_PROD_BUILD_FLAGS[@]}" \
         --build-arg PYTHON_BASE_IMAGE="${AIRFLOW_PYTHON_BASE_IMAGE}" \
-        --build-arg PYTHON_MAJOR_MINOR_VERSION="${PYTHON_MAJOR_MINOR_VERSION}" \
         --build-arg INSTALL_MYSQL_CLIENT="${INSTALL_MYSQL_CLIENT}" \
         --build-arg ADDITIONAL_AIRFLOW_EXTRAS="${ADDITIONAL_AIRFLOW_EXTRAS}" \
         --build-arg ADDITIONAL_PYTHON_DEPS="${ADDITIONAL_PYTHON_DEPS}" \