Disable in-wallet miner for win/macos Travis/Gitian builds

[UdjinM6]

This should lower AV false-positive score for our win/macos release binaries quite a bit.

Before:
https://www.virustotal.com/#/file/f0b6f5833a177d0254ce874a8cdf5b317e648fc05e53db1b6444d0f19f807d9b/detection (17)
After:
https://www.virustotal.com/#/file/30046d2a7bd29b3441df2591ba38f53c559ba8613064e3ed597881da91bcab41/detection (4)

Bitcoin master (for comparison):
https://www.virustotal.com/#/file/1feaf335225525bb492a74929c5bdeb48772fcd4cca02a20d1bc846d906eadf2/detection (6)

Not sure what else could be removed to make every AV happy (suggestions are welcome!) but this PR resolves issues with most major AVs already, so imo it's good enough even if there is nothing else we can do to improve it further.

Downsides:

• 3 more Travis builds;
• have to drop some rpcs in such builds (but "normal" users shouldn't care and advanced ones should be able to build binaries themselves);
• have to disable some unit test in such builds (but similar builds with mining enabled should catch issues if any).

[PastaPastaPasta]

LGTM, but test is currently failing.

[codablock]

Did you try to figure out which part exactly is causing the false-positives? I see that you removed the whole block assembler code (miner.cpp) which then required touching tests. Shouldn't it be enough to remove generateBlocks() and friends (RPCs)?

[UdjinM6]

Excluded generate* rpcs/function only (and corresponding rpc test):
https://www.virustotal.com/#/file/92dc4f1d07b310dde6c0d825af7f7188a9de0b7a8ff2366c4288af876a63a4ef/detection (6, same as bitcoin)

It's weird though, I'm pretty sure that when I tried smth like that earlier I had like 10-ish detections -that's why I started excluding more and more code and finally decided to split builds. Well, anyway... Dropped additional builds Travis now (should be ok-ish to ignore one single generate* test on win/mac imo).

EDIT: also rebased and renamed *mining -> *miner.

[codablock]

LGTM, I'm however wondering why it's needed to use the new configure option in all win+mac builds on Travis? Wouldn't it be enough to only use it on one of the builds to just make sure it builds/links? In the end it's only important to use it in Gitian builds later.

[UdjinM6]

It's basically to make sure that all Gitian builds will/should succeed.

[codablock]

ok, I guess it's better to be on the safe side here instead of realizing that gitian fails AFTER we tag a release :)

utACK

[codablock]

I added the backport-candidate label for 13.x, just in case we decide to do a 13.3 release