Remove started runtime check in RevokeAllThreadLocalAllocationStacks

This check occasionally caused some thread local allocation stacks
to incorrectly not get revoked when multiple threads were allocating
without a started runtime. This showed up in image_test with
compaction enabled when we were initializing classes in the compiler
driver.

Change-Id: I7f28d072feea333c2503e35265ba25c51a6308fe