wrapper: remove xunsetenv()

Remove the unused wrapper function.

Reported-by: Randall S. Becker <rsbecker@nexbridge.com>
Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: carenas

git-compat-util.h

@@ -879,7 +879,6 @@ char *xstrndup(const char *str, size_t len);
 void *xrealloc(void *ptr, size_t size);
 void *xcalloc(size_t nmemb, size_t size);
 void xsetenv(const char *name, const char *value, int overwrite);
-void xunsetenv(const char *name);
 void *xmmap(void *start, size_t length, int prot, int flags, int fd, off_t offset);
 const char *mmap_os_err(void);
 void *xmmap_gently(void *start, size_t length, int prot, int flags, int fd, off_t offset);

wrapper.c

@@ -151,12 +151,6 @@ void xsetenv(const char *name, const char *value, int overwrite)
 		die_errno(_("could not setenv '%s'"), name ? name : "(null)");
 }
 
-void xunsetenv(const char *name)
-{
-	if (!unsetenv(name))
-		die_errno(_("could not unsetenv '%s'"), name ? name : "(null)");
-}
-
 /*
  * Limit size of IO chunks, because huge chunks only cause pain.  OS X
  * 64-bit is buggy, returning EINVAL if len >= INT_MAX; and even in