Remove obsolete lgtm config file #595

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I reviewed the cFS README.md file to see if the feature is in the major future work.
• I performed a cursory search to see if the feature request is relevant, not redundant, nor in conflict with other tickets.

Is your feature request related to a problem? Please describe.
No longer using LGTM, replaced by CodeQL/GitHub scanning.

Describe the solution you'd like
Remove obsolete .lgtm.yml file

Describe alternatives you've considered
None

Additional context
None

Requester Info
Jacob Hageman - NASA/GSFC