refactor: Remove now-unnecessary express & http-proxy-middleware packages (#437)

I was investigating some of the test failures in https://github.com/coder/coder/pull/429 - and realized that we actually don't need the `http-proxy-middleware` package anymore (or the `express` package). Of course - the failures were unrelated to that change, so this doesn't fix the CI failures that were encountered.

`http-proxy-middleware` and `express` were needed for our custom NextJS dev server, but that code was removed in #348 , so those dependencies are no longer explicitly required. We should just remove them to avoid the maintenance overhead.

Another clean-up / follow-up from #348

site/package.json

@@ -51,11 +51,9 @@
     "eslint-plugin-no-storage": "1.0.2",
     "eslint-plugin-react": "7.29.4",
     "eslint-plugin-react-hooks": "4.3.0",
-    "express": "4.17.3",
     "formik": "2.2.9",
     "history": "5.3.0",
     "html-webpack-plugin": "5.5.0",
-    "http-proxy-middleware": "2.0.3",
     "jest": "27.5.1",
     "jest-junit": "13.0.0",
     "jest-runner-eslint": "1.0.0",

site/yarn.lock

@@ -6461,7 +6461,7 @@ expect@^27.5.1:
     jest-matcher-utils "^27.5.1"
     jest-message-util "^27.5.1"
 
-express@4.17.3, express@^4.17.1:
+express@^4.17.1:
   version "4.17.3"
   resolved "https://registry.yarnpkg.com/express/-/express-4.17.3.tgz#f6c7302194a4fb54271b73a1fe7a06478c8f85a1"
   integrity sha512-yuSQpz5I+Ch7gFrPCk4/c+dIBKlQUxtgwqzph132bsT6qhuzss6I8cLJQz7B3rFblzd6wtcI0ZbGltH/C4LjUg==
@@ -7589,7 +7589,7 @@ http-proxy-agent@^4.0.1:
     agent-base "6"
     debug "4"
 
-http-proxy-middleware@2.0.3, http-proxy-middleware@^2.0.0:
+http-proxy-middleware@^2.0.0:
   version "2.0.3"
   resolved "https://registry.yarnpkg.com/http-proxy-middleware/-/http-proxy-middleware-2.0.3.tgz#5df04f69a89f530c2284cd71eeaa51ba52243289"
   integrity sha512-1bloEwnrHMnCoO/Gcwbz7eSVvW50KPES01PecpagI+YLNLci4AcuKJrujW4Mc3sBLpFxMSlsLNHS5Nl/lvrTPA==