8390499: Clean up suspicious bailout in ciMethod::find_monomorphic_target

[merykitty]

Hi,

This PR removes a suspicious place where we bail out of devirtualization. It is suspicious because it is either unnecessary, or it is too late as we have returned root_m in various places. Looking at Dependencies::find_unique_concrete_method, it is also clear that the implementation does not look at the name or the signature, but the vtable or itable index of the method to decide that it is the correct target.

Testing:

• tier1-4,hs-comp-stress

Please take a look and let me know what you think, thanks a lot.

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• JDK-8390499: Clean up suspicious bailout in ciMethod::find_monomorphic_target (Enhancement - P4)

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