Dont keep around scoped allocated ArtMethod after thread suspension.

Those methods are used after thread suspension, and their eg
declaring class is read. Because the GC does not see these methods,
the declaring class can move and the code will then access a stalled
pointer.

Test: test-art-host, ART_TEST_GC_STRESS=true/false
Test: 690-default-smali
Change-Id: I632197bc51f0da1dcf33b08195e8cfa4ccd73188