Remove implicit/explicit heading auto-formatting

See #895 (comment)

> Before Go 1.19, headings were identified implicitly by single-line paragraphs satisfying certain conditions, most notably the lack of any terminating punctuation.
>
> Gofmt reformats [lines treated as implicit headings](https://github.com/golang/proposal/blob/master/design/51082-godocfmt.md#headings) by earlier versions of Go to use # headings instead. If the reformatting is not appropriate—that is, if the line was not meant to be a heading—the easiest way to make it a paragraph is to introduce terminating punctuation such as a period or colon, or to break it into two lines.
>
> *-- https://go.dev/doc/comment#headings*

Author: MadLittleMods

tests/msc3902/federation_room_join_partial_state_test.go

@@ -4287,7 +4287,7 @@ type partialStateJoinResult struct {
 
 // beginPartialStateJoin has a test user attempt to join the given room.
 //
-// # It returns a partialStateJoinResult
+// It returns a partialStateJoinResult.
 //
 // When this method completes, the /join request will have completed, but the
 // state has not yet been re-synced. To allow the re-sync to proceed, call