mkcert-master: remove in favor of "brew gomod filippo.io/mkcert@master"

See https://blog.filippo.io/install-go-tools-from-modules-with-brew-gomod/

mkcert-master.rb

@@ -1,17 +0,0 @@
-# Copyright 2018 The mkcert Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style
-# license that can be found in the LICENSE file.
-
-class MkcertMaster < Formula
-	desc "Simple tool to make locally trusted development certificates"
-	homepage "https://github.com/FiloSottile/mkcert"
-	head "https://github.com/FiloSottile/mkcert.git"
-
-	depends_on "go" => :build
-
-	def install
-		ENV["GOPATH"] = HOMEBREW_CACHE/"go_cache"
-		system "go", "build", "-o", bin/"mkcert"
-		prefix.install_metafiles
-	end
-end