[mlir][ArmSME][test] Use `only-if-required-by-ops` rather than...

[mlir][ArmSME][test] Use `only-if-required-by-ops` rather than `enable_arm_streaming_ignore` (NFC) (#75209)

This moves the fix out of the IR and into the pass description, which
seems nicer. It also works as an integration test for the
`only-if-required-by-ops` flag :)