This change implements the information provided in these slither
issues:
https://github.com/crytic/slither/issues/1408
https://github.com/crytic/slither-action/issues/38

Apparently 'fail_pedantic' defaults to true, which overrides the
'exclude_*' settings and causes failures on optimization and
informational severity findings.

As is this config should:
1. Fail only on High severity findings
2. Print Medium severity findings but not fail on them.

This commit also deletes the findings in the slither db which
were less than high severity. They are now simply ignored via this
corrected config.