Delete .lgtm.yml: LGTM.com will figure things out automatically

[sj]

Now FastSim is using cmake for its build process, there is no longer any need for an .lgtm.yml file with build instructions for LGTM.com Python and C/C++ analysis.

• test code in directories called tests will automatically be classified as such
• documentation only needs to be classified as such if it lives in source code files; any non-code will not be analysed by LGTM
• the numpy Debian/Ubuntu package comes preinstalled in the Python analysis environment
• all of the Debian dependencies for the C/C++ build are automatically detected (and installed) at build time. If you'd like to know how that works, please read our blog post.
• the other cmake and make build commands are all detected and run automatically

I've already tested this on the LGTM staging environment: all works! As soon as this PR is merged (and .lgtm.yml is deleted), I can kick off another C/C++ build and results should be in soon.

(full disclosure: I'm part of the team that built LGTM.com)

[sj]

Note that the Python analysis failure in this pull request is due to the fact that the base commit (current master) cannot be analysed. This means that LGTM can't compare the current state of the Python code base to the new state, and therefore can't comment on whether there are any new or fixed alerts in this PR.

[sj]

Thanks for merging. C/C++ analysis is now in progress. As soon as the latest commit in the FastSim repository has been analysed, automated code review for C/C++ code should start straight away (alongside the existing automatic review for Python).