doc: fix minor typos (extra/duplicated words)

Following are several fixes for duplicated words ("of of") and one
case where an extra article ("a") slipped in.

Signed-off-by: Evan Zacks <zackse@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-cat-file.txt

@@ -192,7 +192,7 @@ newline. The available atoms are:
 	The 40-hex object name of the object.
 
 `objecttype`::
-	The type of of the object (the same as `cat-file -t` reports).
+	The type of the object (the same as `cat-file -t` reports).
 
 `objectsize`::
 	The size, in bytes, of the object (the same as `cat-file -s`

Documentation/git-checkout.txt

@@ -38,7 +38,7 @@ $ git checkout -b <branch> --track <remote>/<branch>
 ------------
 +
 You could omit <branch>, in which case the command degenerates to
-"check out the current branch", which is a glorified no-op with a
+"check out the current branch", which is a glorified no-op with
 rather expensive side-effects to show only the tracking information,
 if exists, for the current branch.
 

Documentation/git-notes.txt

@@ -171,7 +171,7 @@ OPTIONS
 	object that does not have notes attached to it.
 
 --stdin::
-	Also read the object names to remove notes from from the standard
+	Also read the object names to remove notes from the standard
 	input (there is no reason you cannot combine this with object
 	names from the command line).
 

Documentation/git-update-index.txt

@@ -153,7 +153,7 @@ you will need to handle the situation manually.
 +
 Version 4 performs a simple pathname compression that reduces index
 size by 30%-50% on large repositories, which results in faster load
-time. Version 4 is relatively young (first released in in 1.8.0 in
+time. Version 4 is relatively young (first released in 1.8.0 in
 October 2012). Other Git implementations such as JGit and libgit2
 may not support it yet.