chore: Remove @types/terser-webpack-plugin dependency (#158)

A typical userscript doesn't need it because it doesn't import anything from the `terser-webpack-plugin` package; I therefore consider this a backward-compatible change.

I did this:

    $ npm why @types/terser-webpack-plugin
    @types/terser-webpack-plugin@2.2.0
    node_modules/@types/terser-webpack-plugin
      @types/terser-webpack-plugin@"^2.2.0" from the root project

    $ npm remove @types/terser-webpack-plugin

    $ npm install --save-dev --save-exact @types/terser-webpack-plugin@2.2.0

package.json

@@ -71,6 +71,7 @@
   "sideEffects": false,
   "devDependencies": {
     "@types/jest": "29.5.12",
+    "@types/terser-webpack-plugin": "2.2.0",
     "@typescript-eslint/eslint-plugin": "^5.62.0",
     "@typescript-eslint/parser": "^5.62.0",
     "cli-confirm": "^1.0.1",
@@ -90,7 +91,6 @@
   },
   "dependencies": {
     "@types/sass": "^1.16.0",
-    "@types/terser-webpack-plugin": "^2.2.0",
     "@types/webpack": "^4.39.9",
     "css-loader": "^3.2.0",
     "lines-unlines": "^1.0.0",