Replace OSX_ARM64_ABI define with a runtime flag.

[sandreenko]

• Delete DEBUG_ARG_SLOTS code. It was added to check that the previous behavior for supported platforms was preserved with Apple Arm64 changes. Once we get a ci and pass all tests on arm64 apple we should get rid of it, so we don't have any special fields in jit internal structures for !OSX_ARM64_ABI.

• Replace OSX_ARM64_ABI usages with runtime flag, something like #ifdef ARM64 && UNIX -> checkVMflag;

• Revert changes from Add OSX arm64 jit. #45467

[sandreenko]

cc @davidwrighton