tombstoned: clean up TODO on anr writes

audit logs indicate that "append" is still used, but not write.

From ToT master:
avc: granted { append } for comm="tombstoned" scontext=u:r:tombstoned:s0
tcontext=u:object_r:anr_data_file:s0 tclass=file

Bug: 32064548
Test: build
Change-Id: Id05853a8ae38b84deed4d8bcca5a72c64ce7fd7e