Don't require users of src/port/gettimeofday.c to initialize it.

Commit 8001fe67a3 introduced this
requirement, but per discussion, we want to avoid requirements of
this type to make things easier on the calling code.  An especially
important consideration is that this may be used in frontend code,
not just the backend.

Asif Naeem, reviewed by Michael Paquier

src/include/port.h

@@ -328,8 +328,6 @@ extern FILE *pgwin32_popen(const char *command, const char *type);
 #ifndef HAVE_GETTIMEOFDAY
 /* Last parameter not used */
 extern int	gettimeofday(struct timeval * tp, struct timezone * tzp);
-/* On windows we need to call some backend start setup for accurate timing */
-extern void init_win32_gettimeofday(void);
 #endif
 #else							/* !WIN32 */