Stop extending from TSLint's ruleset in the published ruleset

[JoshuaKGoldberg]

Followup to #309 - it's confusing to many users that "extends": ["tslint-microsoft-contrib"] includes our rules extended from TSLint itself. This should be removed in 7.0.

Community packages should just be a set of rules; there's no reason why extending their rules would have any opinion on the core rules brought in with them.