[jax] Simplify test_closed_over_constant_sharded_and_cache_hit in pjit_test
Remove mock spy on ExecuteReplicated.__call__ from
test_closed_over_constant_sharded_and_cache_hit. This mocking is
too complex for the little test coverage it adds.
Testing pjit with closed-over constants directly validates
cache misses (cpp=1), output values, sharding,
and fastpath cache hits (cpp=0) cleanly without
monkey-patching internal runtime methods. The only
thing we are dropping from coverage is that the arguments
are passed properly sharded.
PiperOrigin-RevId: 1004464715