mmap: remove unnecessary assertion

64 bit types are always 64 bit.

src/win32/map.c

@@ -99,8 +99,6 @@ int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offs
 		return -1;
 	}
 
-	assert(sizeof(git_off_t) == 8);
-
 	off_low = (DWORD)(page_start);
 	off_hi = (DWORD)(page_start >> 32);
 	out->data = MapViewOfFile(out->fmh, view_prot, off_hi, off_low, len);