use parcel's builtin css optimizer

because it seems to work fine now

frontend/.parcelrc

@@ -3,14 +3,6 @@
     "transformers": {
         "*.{ts,tsx}": [
             "@parcel/transformer-typescript-tsc"
-        ],
-        "*.css": [
-            "@parcel/transformer-postcss"
-        ]
-    },
-    "optimizers": {
-        "*.css": [
-            "@parcel/optimizer-cssnano"
         ]
     }
 }

frontend/.postcssrc

@@ -1,5 +0,0 @@
-{
-    "plugins": {
-        "autoprefixer": true
-    }
-}

frontend/package.json

@@ -14,7 +14,6 @@
         "@typescript-eslint/eslint-plugin": "^5.12.0",
         "@typescript-eslint/parser": "^5.12.0",
         "@wojtekmaj/enzyme-adapter-react-17": "^0",
-        "autoprefixer": "^10.4.2",
         "enzyme": "^3.11.0",
         "eslint": "^8.9.0",
         "eslint-config-prettier": "^8.3.0",
@@ -30,7 +29,6 @@
         "jest": "^27.5.1",
         "parcel": "^2.3.1",
         "pluralize": "^8.0.0",
-        "postcss": "^8.4.6",
         "prettier": "^2.5.1",
         "prettier-eslint": "^13.0.0",
         "process": "^0.11.10",
@@ -47,8 +45,6 @@
         "spark-md5": "^3.0.2",
         "ts-jest": "^27.1.3",
         "typescript": "^4.5.5",
-        "@parcel/optimizer-cssnano": "^2.4.1",
-        "@parcel/transformer-css-experimental": "^2.3.2",
         "@parcel/transformer-typescript-tsc": "^2.4.1"
     },
     "devDependencies": {