Python: bump minimum version to 3.10

Since Python 3.10 is now supported on all platform,
bump the minimum version to reduce the number of Python versions that
need to be supported simultaneously.

Reviewed By: LazyDodo, sybren, mont29, brecht

Ref D13943

source/blender/python/mathutils/mathutils.c

@@ -90,11 +90,7 @@ Py_hash_t mathutils_array_hash(const float *array, size_t array_len)
   x = 0x345678UL;
   i = 0;
   while (--len >= 0) {
-#if PY_VERSION_HEX >= 0x30a0000 /* Version: 3.10. */
     y = _Py_HashDouble(NULL, (double)(array[i++]));
-#else
-    y = _Py_HashDouble((double)(array[i++]));
-#endif
     if (y == -1) {
       return -1;
     }