x86_64: remove subtype check from invoke-virtual fast path.

After aosp/3248173 and aosp/3250172 a MH object with
invoke-virtual kind can target only virtual methods. As there is
callsite check against MH type no receiver checks are needed.

That's in line with JVMS 4.4.8.

Bug: 297147201

Test: ./art/test/testrunner/testrunner.py --host --64 --optimizing -b
Test: ./art/test.py --host -g
Test: CtsLibcoreTestCases
Test: CtsLibcoreOjTestCases

Change-Id: I2c12760a75b83ddf7cc21d34bcc8bb58621e6cca