Arm backend: Remove build_quantized_ops_aot_lib.sh (#10350)

This lib is built by default when installing executorch, so use that
instead of building our own version. The the version built by executorch
however has an extra dependency on _portable_lib.cpython-310, which
needs to be loaded as well.

Also removes all mentions of this script in related files.

Signed-off-by: Adrian Lundell <adrian.lundell@arm.com>