fast-import doc: remove suggested 16-parent limit

Merges with an absurd number of parents are still a bad idea because
they do not render well in tools like gitk, but if they are present
in the repository being imported into git then there's no need to
avoid reproducing them faithfully.

In olden times, before v1.6.0-rc0~194 (2008-06-27), git commit-tree
and higher-level tools built on top of it were limited to writing 16
parents for a commit.  Nowadays normal git operations are happy to
write more parents when asked, so the motivation for this note in the
fast-import documentation is gone and we can remove it.
Signed-off-by: NJonathan Nieder <jrnieder@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-fast-import.txt

@@ -504,10 +504,6 @@ omitted when creating a new branch, the first `merge` commit will be
 the first ancestor of the current commit, and the branch will start
 out with no files.  An unlimited number of `merge` commands per
 commit are permitted by fast-import, thereby establishing an n-way merge.
-However Git's other tools never create commits with more than 15
-additional ancestors (forming a 16-way merge).  For this reason
-it is suggested that frontends do not use more than 15 `merge`
-commands per commit; 16, if starting a new, empty branch.
 
 Here `<commit-ish>` is any of the commit specification expressions
 also accepted by `from` (see above).