Unlink DevTools submodule and remove references

we don't need this as a submodule anymore, since it's not used in the core.

.gitmodules

@@ -1,6 +1,3 @@
-[submodule "tests/plugins/DevTools"]
-	path = tests/plugins/DevTools
-	url = https://github.com/pmmp/DevTools.git
 [submodule "build/php"]
 	path = build/php
 	url = https://github.com/pmmp/php-build-scripts.git

.php-cs-fixer.php

@@ -5,7 +5,6 @@ $finder = PhpCsFixer\Finder::create()
 	->in(__DIR__ . '/build')
 	->in(__DIR__ . '/tests')
 	->in(__DIR__ . '/tools')
-	->notPath('plugins/DevTools')
 	->notName('PocketMine.php');
 
 return (new PhpCsFixer\Config)

composer.json

@@ -79,7 +79,6 @@
       "sort-packages": true
    },
    "scripts": {
-      "make-devtools": "@php -dphar.readonly=0 tests/plugins/DevTools/src/ConsoleScript.php --make ./ --relative tests/plugins/DevTools --out plugins/DevTools.phar",
       "make-server": [
          "@composer install --no-dev --classmap-authoritative --ignore-platform-reqs",
          "@php -dphar.readonly=0 build/server-phar.php"