[UpdateTestChecks][llvm-mca] Use common.itertests in update_mca_test_checks (#67477)

common.itertests has useful functionality such as skipping test case if
it starts with UTC_AVOID comment string. It also does some of the
functionality, such as skipping test file pattern if not found, that was
duplicated by update_mca_test_checks.

This patch uses this function to take advantage of extra behavior and
remove duplication.