patch 8.2.3987: 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 fdcd6d1..a30ff8b 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -1050,7 +1050,7 @@
     if (*regparse == '\\')
 	regparse++;	// Allow either \{...} or \{...\}
     if (*regparse != '}')
-	EMSG2_RET_FAIL(_("E554: Syntax error in %s{...}"),
+	EMSG2_RET_FAIL(_(e_syntax_error_in_str_curlies),
 						       reg_magic == MAGIC_ALL);
 
     /*