Make restoreCallingIdentity() @CriticalNative.

The validation check that might throw an exception is almost a decade
old at this point, and isn't likely to be hit.  In addition, the
recently added "AndroidFrameworkBinderIdentity" Error Prone checker
ensures that clients working with these identities are well-behaved.

Removing this exception code is what enables @CriticalNative.

Bug: 171078335
Test: none
Change-Id: Ib4cc9becf325979a97a9b0e58ac2277f3b226aaa