Delete socket file if it exists. Fixes #3085.

[talmeme]

#3085: If Unix domain socket file exists then Vapor crashes when starting instead of taking over the socket file.

This PR fixes by deleting the socket file if it exists.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.77%. Comparing base (823f20c) to head (5755b2c).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3146      +/-   ##
==========================================
- Coverage   76.82%   76.77%   -0.05%     
==========================================
  Files         211      211              
  Lines        8096     8096              
==========================================
- Hits         6220     6216       -4     
- Misses       1876     1880       +4     

Files	Coverage Δ
Sources/Vapor/HTTP/Server/HTTPServer.swift	80.49% <100.00%> (ø)

... and 1 file with indirect coverage changes

[0xTim]

Thanks! Sorry for the delay in this - do you think it would be possible to write a test for this?