*.[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>
diff --git a/run-command.h b/run-command.h
index a695069..31f6f2e 100644
--- a/run-command.h
+++ b/run-command.h
@@ -55,7 +55,7 @@ struct child_process {
 #define CHILD_PROCESS_INIT { NULL, ARGV_ARRAY_INIT, ARGV_ARRAY_INIT }
 void child_process_init(struct child_process *);
 void child_process_clear(struct child_process *);
-extern int is_executable(const char *name);
+int is_executable(const char *name);
 
 int start_command(struct child_process *);
 int finish_command(struct child_process *);
@@ -67,10 +67,10 @@ int run_command(struct child_process *);
  * or disabled. Note that this points to static storage that will be
  * overwritten by further calls to find_hook and run_hook_*.
  */
-extern const char *find_hook(const char *name);
+const char *find_hook(const char *name);
 LAST_ARG_MUST_BE_NULL
 extern int run_hook_le(const char *const *env, const char *name, ...);
-extern int run_hook_ve(const char *const *env, const char *name, va_list args);
+int run_hook_ve(const char *const *env, const char *name, va_list args);
 
 #define RUN_COMMAND_NO_STDIN 1
 #define RUN_GIT_CMD	     2	/*If this is to be git sub-command */