Remove LGTM from documents

[ArielSAdams]

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.
LGTM is no longer used as a testing method for cFS.

Describe the solution you'd like
Remove the mention of LGTM in documents such as SECURITY.md and README.md.

Describe alternatives you've considered
Keep as is.

Additional context
LGTM will be shut down in December of 2022.

Requester Info
Ariel Adams, MCSG Tech.