ASSERT dynamo_exited in fd_table_remove

If I pass -satisfy_w_xor_x to the tool.drcacheoff.gencode test, I hit an assert dynamo_exited in fd_table_remove(). The test does a full DR detach followed by dr_standalone_init() + dr_standalone_exit(). The full detach clears dynamo_exited for re-attach, and the standalone exit closes a file due to the -satisfy_w_xor_x mappings and hits the assert.

I think just adding || standalone_library to the assert is the right fix.