[bcl] Fix a few hardcoded socket ports in tests (#5471)

[bcl] Fix a few hardcoded socket ports in tests (#5471)

* [System] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.

* [System.Runtime.Remoting] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.

Additionally remove a copy of RemotingServicesTest.cs from corlib
which also exists in System.Runtime.Remoting in updated form.

* [System.ServiceModel] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.

* [System.Net.Http] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.

The additional "keep-alive" header in Send_Complete_NoContent() and
Send_Transfer_Encoding_Chunked() is because we were using the same
port for all tests before so other tests would clear the header.
This doesn't happen now that we use distinct test ports.

* [System.ServiceModel.Web] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.