patch 8.2.1460: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more messages into errors.h.
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 2550f0e..c61f575 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -3842,7 +3842,7 @@
     if (search_regcomp(pat, RE_SUBST, which_pat, SEARCH_HIS, &regmatch) == FAIL)
     {
 	if (subflags.do_error)
-	    emsg(_(e_invcmd));
+	    emsg(_(e_invalid_command));
 	return;
     }
 
@@ -4816,7 +4816,7 @@
 
     if (search_regcomp(pat, RE_BOTH, which_pat, SEARCH_HIS, &regmatch) == FAIL)
     {
-	emsg(_(e_invcmd));
+	emsg(_(e_invalid_command));
 	return;
     }