scip_backend: Remove use of deprecated sage.ext.memory_allocator

[mkoeppe]

... and other unused imports.

CC: @dimpase @fchapoton

Component: linear programming

Author: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/34941

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1 +1 @@
-
+... and other unused imports.

[mkoeppe]

Branch: u/mkoeppe/scip_backend__remove_use_of_deprecated_sage_ext_memory_allocator

[mkoeppe]

New commits:

25f84e3

src/sage/numerical/backends/scip_backend.pyx: Remove unused imports

[mkoeppe]

Commit: 25f84e3

[mkoeppe]

Author: Matthias Koeppe

[mkoeppe]

comment:4

The test failure in sage/schemes/elliptic_curves/ell_curve_isogeny.py is unrelated.