Remove changes/bug7129

Our convention is that we use the changelog to note release-to-release
changes; we don't need to add changelog entries for bugs that didn't
appear in any released version of Tor.  (By convention, we sometimes
say "this bug does not appear in any released version of Tor" or words
to that effect in the commit message so that when Roger goes to make
sure the changelog is right, he knows not to expect a changelog entry
for that part.)

changes/bug7129

- o Minor bugfixes:
-   - Fix mal-merge of channels that ORed END_CIRC_REASON_CHANNEL_CLOSED into
-     reason codes in circuit_truncated().
-   - Fix unknown reason warning in circuit_end_reason_to_control_string()
-     to use LD_PROTOCOL rather than LD_BUG when the bad reason originated
-     elsewhere.