Documentation: fix various repeat word typos

Inspired by 24966cd982 ("doc: fix repeated words", 08-09-2019),
I ran "egrep -R "\<([a-zA-Z]+)\> \<\1\>" ./Documentation/*" to
find current cases of repeated words such as "the the" that were
quite clearly typos.

There were many false positives reported, such as "really really"
or valid uses of "that that" which I left alone.

Signed-off-by: Jacob Stopak <jacob@initialcommit.io>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/CodingGuidelines

@@ -606,7 +606,7 @@ Writing Documentation:
     avoidance of gendered pronouns.
 
   - When it becomes awkward to stick to this style, prefer "you" when
-    addressing the the hypothetical user, and possibly "we" when
+    addressing the hypothetical user, and possibly "we" when
     discussing how the program might react to the user.  E.g.
 
       You can use this option instead of --xyz, but we might remove