shared.c: Remove unused "linux/limits.h" include

This isn't used anywhere and prevents the code from being compiled on
other platforms, such as *BSD.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>

shared.c

@@ -8,7 +8,6 @@
 
 #include "cgit.h"
 #include <stdio.h>
-#include <linux/limits.h>
 
 struct cgit_repolist cgit_repolist;
 struct cgit_context ctx;