patch 8.1.2171: mouse support not always available

Problem:    Mouse support not always available.
Solution:   Enable mouse support also in tiny version.  Do not define
            FEAT_MOUSE_XTERM on MS-Windows (didn't really work).
diff --git a/src/os_win32.h b/src/os_win32.h
index 2169bd3..ac89911 100644
--- a/src/os_win32.h
+++ b/src/os_win32.h
@@ -62,7 +62,7 @@
 #endif
 
 #define USE_FNAME_CASE		/* adjust case of file names */
-#if !defined(FEAT_CLIPBOARD) && defined(FEAT_MOUSE)
+#if !defined(FEAT_CLIPBOARD)
 # define FEAT_CLIPBOARD		/* include clipboard support */
 #endif
 #if defined(__DATE__) && defined(__TIME__)