Remove CS server support from CDNClient

[xPaw]

I kept AuthenticateDepot and internal dictionaries to track keys and cdn keys for consumers that don't implement their own.

FetchServerListAsync is removed by #759

[azuisleet]

This is a breaking API change:

• Methods are removed of course
• The CDNClient previously tracked a currently connected server, but now the new API has the user pass in the Server endpoint

[azuisleet]

The trailing slash in the URL builder should be user supplied:

200:
https://edge.steam-dns.top.comcast.net:443/depot/232256/manifest/6917145573004583473/5?params

404:
https://edge.steam-dns.top.comcast.net:443/depot/232256/manifest/6917145573004583473/5/?params

[codecov]

Codecov Report

Merging #725 into master will increase coverage by <.01%.
The diff coverage is 21.42%.

@@            Coverage Diff             @@
##           master     #725      +/-   ##
==========================================
+ Coverage   22.62%   22.63%   +<.01%     
==========================================
  Files          94       94              
  Lines        9379     9561     +182     
  Branches      772      805      +33     
==========================================
+ Hits         2122     2164      +42     
- Misses       7128     7265     +137     
- Partials      129      132       +3

Impacted Files	Coverage Δ
SteamKit2/SteamKit2/Steam/CDNClient.cs	14.57% <21.42%> (-1.16%)	⬇️
...eamKit2/SteamKit2/Steam/SteamClient/SteamClient.cs	44.6% <0%> (-0.9%)	⬇️
SteamKit2/SteamKit2/Steam/SteamClient/Callbacks.cs	0% <0%> (ø)	⬆️
.../Steam/Handlers/SteamNetworking/SteamNetworking.cs
...amKit2/Steam/Handlers/SteamNetworking/Callbacks.cs
SteamKit2/SteamKit2/Steam/UFSClient/UFSClient.cs	7.6% <0%> (ø)
SteamKit2/SteamKit2/Steam/UFSClient/Callbacks.cs	13.95% <0%> (ø)
SteamKit2/SteamKit2/Util/HardwareUtils.cs	27.23% <0%> (+1.87%)	⬆️
SteamKit2/SteamKit2/Util/Utils.cs	28.04% <0%> (+3.04%)	⬆️
... and 2 more

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[azuisleet]

OK. Breaking API changes.

[yaakov-h]

Technically it's actually a CDNClient now and not also a CSClient. 😄

[yaakov-h]

This will also need corresponding changes to DepotDownloader... I tried to take a look but I'm way in over my head with that.

[yaakov-h]

@xPaw merge conflict with yourself 😛

[xPaw]

Rebased and squashed.