src: remove VS 2013 compatibility hacks

[bnoordhuis]

We can remove some Visual Studio 2013-specific workarounds now that
support for that compiler has officially been dropped.

Refs: #7484
Refs: #8049

("has been dropped" == future tense.)

The last commit is something I can drop if people feel it's less readable.

CI: https://ci.nodejs.org/job/node-test-pull-request/3625/ (expected to fail on the vs2013 buildbots.)

[jasnell]

more or less rubber stamp LGTM if CI is green where it should be

[bnoordhuis]

There were some rather strange errors on the fedora22 and fedora23 builbots. New CI, just in case: https://ci.nodejs.org/job/node-test-pull-request/3628/

[joaocgreis]

Working on the bits for not using VS2013 on v6 and after, already working for the compile job: https://ci.nodejs.org/job/node-test-pull-request/3669/ But the test job will have to run on machines with VS2013, because we still support building native modules with that. Will have to work more on that.

It's great to have this work ready, but perhaps this should only land after we have the release servers ready, so that non-LTS releases of v6 don't have to work around this.

[bnoordhuis]

That's fine, there is no rush to land this.

[joaocgreis]

#8412 is my suggestion to unblock this. After it lands, CI for this should be all green: test machines (vcbuild noprojgen nobuild nosign test-ci) will no longer try to find Visual Studio, node-gyp will handle that independently.

[joaocgreis]

#8412 has landed, here is a passing CI: https://ci.nodejs.org/job/node-test-commit/4954/

Changes in vcbuild.bat now LGTM.

[bnoordhuis]

Rebased: https://ci.nodejs.org/job/node-test-pull-request/4070/

[jasnell]

LGTM