Remove display_erros()

do_shell() in Nvim uses the Nvim UI, not the tty directly, so
display_errors() is not necessary anymore.

src/nvim/ex_cmds.c

@@ -1391,9 +1391,6 @@ do_shell(
   msg_row = Rows - 1;
   msg_col = 0;
 
-  // display any error messages now
-  display_errors();
-
   apply_autocmds(EVENT_SHELLCMDPOST, NULL, NULL, FALSE, curbuf);
 }