patch 8.2.4012: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move the last error messages to errors.h.
diff --git a/src/register.c b/src/register.c
index eaabbd5..d61a5d0 100644
--- a/src/register.c
+++ b/src/register.c
@@ -2780,8 +2780,7 @@
 	    s = (char_u *)"";
 	else if (strings[1] != NULL)
 	{
-	    emsg(_("E883: search pattern and expression register may not "
-			"contain two or more lines"));
+	    emsg(_(e_search_pattern_and_expression_register_may_not_contain_two_or_more_lines));
 	    return;
 	}
 	else