*: fix typos which duplicate a word

Fix typos in code comments which repeat various words.  Most of the
cases are simple in that they repeat a word that usually cannot be
repeated in a grammatically correct sentence.  Just remove the
incorrectly duplicated word in these cases and rewrap text, if needed.

A tricky case is usage of "that that", which is sometimes grammatically
correct.  However, an instance of this in "t7527-builtin-fsmonitor.sh"
doesn't need two words "that", because there is only one daemon being
discussed, so replace the second "that" with "the".

Reword code comment "entries exist on on-disk index" in function
update_one in file cache-tree.c, by replacing incorrect preposition "on"
with "in".

Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -1270,7 +1270,7 @@ static int parse_branchname_arg(int argc, const char **argv,
 	 *       between A and B, A...B names that merge base.
 	 *
 	 *   (b) If <something> is _not_ a commit, either "--" is present
-	 *       or <something> is not a path, no -t or -b was given, and
+	 *       or <something> is not a path, no -t or -b was given,
 	 *       and there is a tracking branch whose name is <something>
 	 *       in one and only one remote (or if the branch exists on the
 	 *       remote named in checkout.defaultRemote), then this is a

builtin/submodule--helper.c

@@ -3219,9 +3219,8 @@ static void die_on_index_match(const char *path, int force)
 		ensure_full_index(&the_index);
 
 		/*
-		 * Since there is only one pathspec, we just need
-		 * need to check ps_matched[0] to know if a cache
-		 * entry matched.
+		 * Since there is only one pathspec, we just need to
+		 * check ps_matched[0] to know if a cache entry matched.
 		 */
 		for (i = 0; i < the_index.cache_nr; i++) {
 			ce_path_match(&the_index, the_index.cache[i], &ps,