patch 8.2.1019: mapping <M-S-a> does not work in the GUI

Problem:    Mapping <M-S-a> does not work in the GUI.
Solution:   Move the logic to remove the shift modifier to
            may_remove_shift_modifier() and also use it in the GUI.
diff --git a/src/version.c b/src/version.c
index fdb7c9f..5d7e451 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1019,
+/**/
     1018,
 /**/
     1017,