Remove unnecessary functions from JSMATH. NFC

See the comments at the top of `emscripten/js_math.h` for why JS
versions of these functions are not needed.

As a followup I plan to map `jsmath.c` functions to `em_math.h`
functions instead of using EM_JS here.

See emscripten-core#19284

system/lib/jsmath.c

@@ -23,9 +23,6 @@ CALL_JS_1_TRIPLE(atan, Math.atan)
 CALL_JS_1_TRIPLE(exp, Math.exp)
 CALL_JS_1_TRIPLE(log, Math.log)
 CALL_JS_1_TRIPLE(sqrt, Math.sqrt)
-CALL_JS_1_TRIPLE(fabs, Math.abs)
-CALL_JS_1_TRIPLE(ceil, Math.ceil)
-CALL_JS_1_TRIPLE(floor, Math.floor)
 
 #define CALL_JS_2(cname, jsname, type, casttype) \
   EM_JS(type, JS_##cname, (type x, type y), { return jsname(x, y) }); \
@@ -50,11 +47,6 @@ CALL_JS_1_IMPL_TRIPLE(round, {
   return x >= 0 ? Math.floor(x + 0.5) : Math.ceil(x - 0.5);
 })
 CALL_JS_1_IMPL_TRIPLE(rint,  {
-  function round(x) {
-    return x >= 0 ? Math.floor(x + 0.5) : Math.ceil(x - 0.5);
-  }
+  var round(x) => x >= 0 ? Math.floor(x + 0.5) : Math.ceil(x - 0.5);
   return (x - Math.floor(x) != .5) ? round(x) : round(x / 2) * 2;
 })
-
-double nearbyint(double x) { return rint(x); }
-float nearbyintf(float x) { return rintf(x); }