*.[ch]: remove extern from function declarations using spatch

There has been a push to remove extern from function declarations.
Remove some instances of "extern" for function declarations which are
caught by Coccinelle. Note that Coccinelle has some difficulty with
processing functions with `__attribute__` or varargs so some `extern`
declarations are left behind to be dealt with in a future patch.

This was the Coccinelle patch used:

	@@
	type T;
	identifier f;
	@@
	- extern
	  T f(...);

and it was run with:

	$ git ls-files \*.{c,h} |
		grep -v ^compat/ |
		xargs spatch --sp-file contrib/coccinelle/noextern.cocci --in-place

Files under `compat/` are intentionally excluded as some are directly
copied from external sources and we should avoid churning them as much
as possible.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

delta.h

@@ -13,7 +13,7 @@ struct delta_index;
  * before free_delta_index() is called.  The returned pointer must be freed
  * using free_delta_index().
  */
-extern struct delta_index *
+struct delta_index *
 create_delta_index(const void *buf, unsigned long bufsize);
 
 /*
@@ -21,14 +21,14 @@ create_delta_index(const void *buf, unsigned long bufsize);
  *
  * Given pointer must be what create_delta_index() returned, or NULL.
  */
-extern void free_delta_index(struct delta_index *index);
+void free_delta_index(struct delta_index *index);
 
 /*
  * sizeof_delta_index: returns memory usage of delta index
  *
  * Given pointer must be what create_delta_index() returned, or NULL.
  */
-extern unsigned long sizeof_delta_index(struct delta_index *index);
+unsigned long sizeof_delta_index(struct delta_index *index);
 
 /*
  * create_delta: create a delta from given index for the given buffer
@@ -40,7 +40,7 @@ extern unsigned long sizeof_delta_index(struct delta_index *index);
  * returned and *delta_size is updated with its size.  The returned buffer
  * must be freed by the caller.
  */
-extern void *
+void *
 create_delta(const struct delta_index *index,
 	     const void *buf, unsigned long bufsize,
 	     unsigned long *delta_size, unsigned long max_delta_size);
@@ -75,7 +75,7 @@ diff_delta(const void *src_buf, unsigned long src_bufsize,
  * *trg_bufsize is updated with its size.  On failure a NULL pointer is
  * returned.  The returned buffer must be freed by the caller.
  */
-extern void *patch_delta(const void *src_buf, unsigned long src_size,
+void *patch_delta(const void *src_buf, unsigned long src_size,
 			 const void *delta_buf, unsigned long delta_size,
 			 unsigned long *dst_size);