fix(messages): typo and unwanted truncation in msg_outtrans_long #31669

- Typo/bug in msg_outtrans_long passing string length as "hist" argument.
- Avoid truncating message in msg_outtrans_long with ext_messages (followup to 
  1097d239c3).
- Remove `_hl` from `msg_keep`, `smsg_keep` as there is no non-`_hl` variant.
- `msg_printf_hl` is removed (identical to `smsg` except it sets
  `msg_scroll = true`, seemingly as a caveat to force a more prompt in
  cmdline mode). Move this logic to the only the only place this was
  used in ex_getln.c.

src/nvim/undo.c

@@ -2596,12 +2596,12 @@ static void u_undo_end(bool did_undo, bool absolute, bool quiet)
     check_pos(curbuf, &VIsual);
   }
 
-  smsg_hl_keep(0, _("%" PRId64 " %s; %s #%" PRId64 "  %s"),
-               u_oldcount < 0 ? (int64_t)-u_oldcount : (int64_t)u_oldcount,
-               _(msgstr),
-               did_undo ? _("before") : _("after"),
-               uhp == NULL ? 0 : (int64_t)uhp->uh_seq,
-               msgbuf);
+  smsg_keep(0, _("%" PRId64 " %s; %s #%" PRId64 "  %s"),
+            u_oldcount < 0 ? (int64_t)-u_oldcount : (int64_t)u_oldcount,
+            _(msgstr),
+            did_undo ? _("before") : _("after"),
+            uhp == NULL ? 0 : (int64_t)uhp->uh_seq,
+            msgbuf);
 }
 
 /// Put the timestamp of an undo header in "buf[buflen]" in a nice format.