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/option.c b/src/option.c
index 898068b..d27c73c 100644
--- a/src/option.c
+++ b/src/option.c
@@ -4976,9 +4976,7 @@
      * outputting a few things that the terminal doesn't understand, but the
      * screen will be cleared later, so this is OK.
      */
-#ifdef FEAT_MOUSE_TTY
-    mch_setmouse(FALSE);	    /* switch mouse off */
-#endif
+    mch_setmouse(FALSE);	    // switch mouse off
 #ifdef FEAT_TITLE
     mch_restore_title(SAVE_RESTORE_BOTH);    /* restore window titles */
 #endif