patch 8.2.0822: Vim9: code left over from discovery phase

Problem:    Vim9: code left over from discovery phase.
Solution:   Remove the dead code.
diff --git a/src/ex_cmds.h b/src/ex_cmds.h
index 2d86c5d..f68c4fd 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -396,7 +396,7 @@
 EXCMD(CMD_confirm,	"confirm",	ex_wrongmodifier,
 	EX_NEEDARG|EX_EXTRA|EX_NOTRLCOM|EX_CMDWIN,
 	ADDR_NONE),
-EXCMD(CMD_const,	"const",	ex_const,
+EXCMD(CMD_const,	"const",	ex_let,
 	EX_EXTRA|EX_NOTRLCOM|EX_SBOXOK|EX_CMDWIN,
 	ADDR_NONE),
 EXCMD(CMD_copen,	"copen",	ex_copen,