Fix unstable results in hist method

[SmirnovEgorRu]

After my changes I observed some small differences in results from run to run.
For example, log-loss for HIGGS data set:
1 run: 0.807342768946606615
2 run: 0.807342768708895875

The reason was so easy - guided scheduling instead of static in OpenMP loop. It leads to non-deterministic operations with floating-point numbers.

I have fixed it and now log-loss:
1 run: 0.807342767697801778
2 run: 0.807342767697801778
3 run: 0.807342767697801778

Training time is the same as it were before:
Before time: 2951ms
After time: 2903ms

[SmirnovEgorRu]

Ci contains following error:
tests/python/test_linear.py::TestLinear::test_shotgun terminate called after throwing an instance of 'std::bad_alloc'
[2019-08-13T11:59:10.252Z] what(): std::bad_alloc

I don't sure, that it is my problem, probably some infrastructure issue. Can we restart this?

[hcho3]

See #4716, which already removed guided scheduling.