Reduce number of tests in test_mcsolve.py
Reduce number of tests in test_mcsolve.py

Previously the "known" tests had three tests per case and nine cases,
each of which required a full call to `mcsolve`.  The tests were
"expect-only output is correct", "states-only output is correct",
"expect-and-states output is correct".  Only the last test is necessary
to check if a configuration has produced the correct integration
results, and the other two are smaller, behaviour-type tests.

In order to keep evaluations down, this removes the "x-only" tests from
the full mix-in class, and applies them only to the no-collapse case so
that the behviour is still tested.

On my machine, this reduced the runtime for Cython-enabled tests from
01:56 to 00:59 (mm:ss), and Cython-disabled tests from 01:33 to 00:28.

qutip/qutip,qutip/qutip,cgranade/qutip,cgranade/qutip