patch 8.2.4010: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/regexp.c b/src/regexp.c
index 2dad2b8..115231e 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -2638,7 +2638,7 @@
 	}
 	else
 	{
-	    emsg(_("E864: \\%#= can only be followed by 0, 1, or 2. The automatic engine will be used "));
+	    emsg(_(e_percent_hash_can_only_be_followed_by_zero_one_two_automatic_engine_will_be_used));
 	    regexp_engine = AUTOMATIC_ENGINE;
 	}
     }