*: 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>
diff --git a/cache-tree.c b/cache-tree.c
index c97111c..9af457f 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -405,7 +405,7 @@ static int update_one(struct cache_tree *it,
 		}
 
 		/*
-		 * CE_INTENT_TO_ADD entries exist on on-disk index but
+		 * CE_INTENT_TO_ADD entries exist in on-disk index but
 		 * they are not part of generated trees. Invalidate up
 		 * to root to force cache-tree users to read elsewhere.
 		 */