Master: remove 2 more changes files that are merged in 0.3.0.4-rc

changes/bug21415

-  o Minor bugfix (entry guards):
-    - Silence a BUG() warning when attempting to use a guard whose descriptor
-      we don't know and make this scenario more unlikely to happen. Fixes bug
-      21415; bugfix on 0.3.0.1-alpha.

changes/bug21581

-  o Minor bugfixes (testing):
-    - Restore support for test-network.sh on BSD and other systems without
-      bash. (But use bash if it's available.) This is a workaround until we
-      remove bash-specific code in 19699.
-      Fixes bug 21581; bugfix on 21562, not in any released version of tor.