refactor: Remove unnecessary express & http-proxy-middleware packages

[bryphe-coder]

I was investigating some of the test failures in #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

[codecov]

Codecov Report

Merging #437 (eae3511) into main (5d54647) will increase coverage by 0.29%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #437      +/-   ##
==========================================
+ Coverage   68.07%   68.37%   +0.29%     
==========================================
  Files         159      159              
  Lines        9226     9226              
  Branches       73       73              
==========================================
+ Hits         6281     6308      +27     
+ Misses       2322     2300      -22     
+ Partials      623      618       -5     

Flag	Coverage Δ
unittest-go-macos-latest	62.86% <ø> (+0.25%)	⬆️
unittest-go-ubuntu-latest	67.67% <ø> (+0.20%)	⬆️
unittest-go-windows-2022	62.31% <ø> (+0.01%)	⬆️
unittest-js	64.07% <ø> (ø)

Impacted Files	Coverage Δ
peerbroker/listen.go	81.35% <0.00%> (-2.55%)	⬇️
peer/channel.go	83.62% <0.00%> (-2.34%)	⬇️
coderd/provisionerdaemons.go	57.60% <0.00%> (+0.54%)	⬆️
provisionerd/provisionerd.go	80.69% <0.00%> (+1.47%)	⬆️
peer/conn.go	79.53% <0.00%> (+1.53%)	⬆️
agent/agent.go	69.32% <0.00%> (+2.10%)	⬆️
provisioner/echo/serve.go	57.50% <0.00%> (+2.50%)	⬆️
codersdk/provisionerdaemons.go	61.53% <0.00%> (+3.07%)	⬆️
peerbroker/dial.go	82.45% <0.00%> (+7.01%)	⬆️
provisionersdk/serve.go	43.24% <0.00%> (+8.10%)	⬆️

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[bryphe-coder]

Thanks for the quick review again @kylecarbs !