patch 8.1.1688: old makefiles are no longer useful

Problem:    Old makefiles are no longer useful.
Solution:   Delete the makefiles, they most likely don't work anyway.
diff --git a/src/version.c b/src/version.c
index 69060d5..ddf68db 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1688,
+/**/
     1687,
 /**/
     1686,