lint: remove qt SIGNAL/SLOT lint

I think we are past the point where we need to lint for this, the CPU
can probably be better utilized.

test/lint/lint-qt.sh

@@ -1,20 +0,0 @@
-#!/usr/bin/env bash
-#
-# Copyright (c) 2018 The Bitcoin Core developers
-# Distributed under the MIT software license, see the accompanying
-# file COPYING or http://www.opensource.org/licenses/mit-license.php.
-#
-# Check for SIGNAL/SLOT connect style, removed since Qt4 support drop.
-
-export LC_ALL=C
-
-EXIT_CODE=0
-
-OUTPUT=$(git grep -E '(SIGNAL|, ?SLOT)\(' -- src/qt)
-if [[ ${OUTPUT} != "" ]]; then
-    echo "Use Qt5 connect style in:"
-    echo "$OUTPUT"
-    EXIT_CODE=1
-fi
-
-exit ${EXIT_CODE}