Omit MR link from release notes

When manually handling the release notes (due to rst markup, fixups
etc.), the different MR number for backports causes needless friction.
Remove the reference from release notes and keep it only in changelog
which isn't manually redacted.

(cherry picked from commit 993ba7cc7f)

contrib/gitchangelog/relnotes.rc.py

@@ -46,7 +46,7 @@ body_process = (
         r" :gl:`\3`",
     )
     | ReSub(r"\n*Merge branch '[^']+' into [^\n]+", r"")
-    | ReSub(r"\n*See merge request isc-projects/bind9(!\d+)", r" :gl:`\1`")
+    | ReSub(r"\n*See merge request isc-projects/bind9(!\d+)", r"")
     | Wrap(regexp="\n\n", separator="\n\n")
     | strip
 )