refactor: remove killable

[snitin315]

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

No

Motivation / Use-Case

less deps

Breaking Changes

No

Additional Info

No

[codecov]

Codecov Report

Merging #3657 (6f43ab6) into master (75bafbf) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3657   +/-   ##
=======================================
  Coverage   93.66%   93.67%           
=======================================
  Files          15       15           
  Lines        1311     1312    +1     
  Branches      452      450    -2     
=======================================
+ Hits         1228     1229    +1     
  Misses         76       76           
  Partials        7        7           

Impacted Files	Coverage Δ
lib/Server.js	93.69% <100.00%> (+0.05%)	⬆️
lib/servers/BaseServer.js	100.00% <100.00%> (ø)
lib/servers/SockJSServer.js	97.14% <100.00%> (-0.23%)	⬇️
lib/servers/WebsocketServer.js	91.42% <100.00%> (-0.68%)	⬇️

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