Remove incorrect checks for ShadowFrame in GetLocalInstance

We used to require (and ensure) that GetLocalInstance had a
ShadowFrame to get the 'this' value from a frame. Since then improved
deopt support has made this unneeded. Unfortunately this check was not
removed with the rest of them.

Test: ./test.py --host -j50

Bug: 33616143
Bug: 34414073

Change-Id: I19c49f9d0e71f331f50c79e8ea4d47ed5b1f1d92