do not include the same header twice

A few files include the same header file directly more than once.

As all these headers protect themselves against repeated inclusion
by the "#ifndef FOO_H / #define FOO_H / ... / #endif" idiom, leave
only the first inclusion and remove the later inclusion as a no-op
clean-up.
Signed-off-by: NДилян Палаузов <git-dpa@aegee.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -11,7 +11,6 @@
 #include "run-command.h"
 #include "parse-options.h"
 #include "sigchain.h"
-#include "transport.h"
 #include "submodule.h"
 #include "connected.h"
 #include "argv-array.h"

trailer.c

 #include "cache.h"
 #include "string-list.h"
 #include "run-command.h"
-#include "string-list.h"
 #include "commit.h"
 #include "trailer.h"
 /*

transport-helper.c

@@ -5,7 +5,6 @@
 #include "commit.h"
 #include "diff.h"
 #include "revision.h"
-#include "quote.h"
 #include "remote.h"
 #include "string-list.h"
 #include "thread-utils.h"

userdiff.c

 #include "cache.h"
 #include "userdiff.h"
-#include "cache.h"
 #include "attr.h"
 
 static struct userdiff_driver *drivers;