Drop 32bit support for Linux

[oech3]

It is difficult to find any active Linux distribution for x86 and test it. It could be just dropped before supporting additional arch.

[ayushmanchhabra]

Related: https://lwn.net/Articles/1035727/

IMO, when Chromium or Node stop supporting 32 bit is probably when NW.js will too.

[oech3]

nodejs/node#53184 is about Windows