fixes #2734: improve iOS testing

[incanus]

• Got rid of the heading tracking test. Mocking this is proving too complicated (plus I turned up two GL library bugs in the process) and we do builds often enough to keep manual tabs on this functionality. I just don't think it's worth the hassle to automate, especially given the low risk of functionality breakage.
• Fixed said tracking-related bugs in MGLMapView.
• Removed the external location mocking library to make this more like other test suites.
• Moved to Debug since it runs faster these days.
• Test tweaks for more reliability.
• Enabled all tests. In future, if tests are flapping, we should remove them and ticket replacement, not disable them.

Going to squash/rebase/finalize etc. before merging.

/cc @friedbunny @1ec5

[1ec5]

Good idea.

[friedbunny]

Happy to be rid of the old mock location stuff, was clunky. I'll kick the tires on this a bit now...

[friedbunny]

Travis is failing on testCompassTap:

MapViewTests
  testCompassTap, ((tester.mapView.direction) equal to (180)) failed: ("333.527575343") is not equal to ("180") - setting direction should take effect
  /Users/travis/build/mapbox/mapbox-gl-native/test/ios/MapViewTests.m:99

                   180,
                   @"setting direction should take effect");

     Executed 22 tests, with 1 failure (0 unexpected) in 39.952 (39.976) seconds

And bitrise is failing on testUserTrackingModeFollow:

/Users/vagrant/git/test/ios/MapViewTests.m:651: error: -[MapViewTests testUserTrackingModeFollow] : ((tester.mapView.userLocation.coordinate.latitude) equal to (kMockedLatitude)) failed: ("37.785834") is not equal to ("37.775716") - user location latitude should match mocked latitude
Test Case '-[MapViewTests testUserTrackingModeFollow]' failed (3.688 seconds).

[friedbunny]

Seeing testUserTrackingModeFollow fail locally, as well:

testUserTrackingModeFollow, ((tester.mapView.userLocation.coordinate.latitude) equal to (kMockedLatitude)) failed: ("37.33233141") is not equal to ("37.775716") - user location latitude should match mocked latitude
/mapbox-gl-native/test/ios/MapViewTests.m:651

[incanus]

Yeah, still getting fails here, hardly ever locally, but flapping on Bitrise and Travis. Just rebased off of a243f41 to ditch Travis, though.

[incanus]

Current take here is to:

• Remove user tracking-related tests as just too unstable; ticket as todo.
• Remove currently-disabled metrics tests; ticket as todo.
• Rebase, squash, etc. and merge this sucker.

Refs #2213

/cc @1ec5 @friedbunny @jfirebaugh

[incanus]

This is passing Bitrise and the iOS slice is no longer on Travis, so will prep this for merge now.

[1ec5]

Still getting this failure locally:

MapViewTests
  testCompassTap, ((tester.mapView.direction) equal to (180)) failed: ("226.279000419") is not equal to ("180") - setting direction should take effect
  /path/to/mapbox-gl-native/test/ios/MapViewTests.m:70
                   180,
                   @"setting direction should take effect");

[1ec5]

The failure is being tracked in #2920.