[Docs] remove references to ci scripts in docs

[driazati]

These shouldn't be run outside of Docker as they usually have a bunch of dependencies that would be tedious to describe manually. Typical usage would be inside of tests/scripts/ci.py so they don't need to be manually invoked at all. This came up in https://tvm.apache.org/docs/install/from_source.html#enable-c-tests where task_cpp_unittest.sh requires ninja and sccache to run. It should be replaced with instructions on how to run the tests using gtest's driver directly