patch 8.2.2143: Vim9: dead code in compiling :unlet

Problem:    Vim9: dead code in compiling :unlet.
Solution:   Don't check for "!" a second time.
diff --git a/src/version.c b/src/version.c
index be7e4f0..be8c64a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2143,
+/**/
     2142,
 /**/
     2141,