patch 8.2.3069: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move some error messages to errors.h.  Use clearer names.
diff --git a/src/map.c b/src/map.c
index 9923522..1f935ba 100644
--- a/src/map.c
+++ b/src/map.c
@@ -2717,7 +2717,7 @@
     {
 	case 1: emsg(_(e_invarg));
 		break;
-	case 2: emsg((isabbrev ? _(e_noabbr) : _(e_nomap)));
+	case 2: emsg((isabbrev ? _(e_no_such_abbreviation) : _(e_nomap)));
 		break;
     }
 }