twister: remove toolchain test

We now get toolchain from cmake and can operate even if the toolchain
variant is not set in the envrionment, this test was verifying the old
behavior, so remove. There is not much twister related here to test and
the environment is not setup correctly to run all of this cmake code. We
are testing twister after all.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>