Remove ember-cli-mocha useLintTree configuration option

[notmessenger]

This project uses semver, please check the scope of this pr:

• [x] #none# - documentation fixes and/or test additions
• [ ] #patch# - backwards-compatible bug fix
• [ ] #minor# - adding functionality in a backwards-compatible manner
• [ ] #major# - incompatible API change

Based on the conversations in https://github.com/ember-cli/ember-cli-mocha/issues/105 and https://github.com/ember-cli/ember-cli-eslint/issues/7 as well as this change https://github.com/ember-cli/ember-cli-qunit/commit/425a26eb60fabe919a161f71701dd74046d26c5b#diff-04c6e90faac2675aa89e2176d2eec7d8 the use of this configuration option was for the transition state between JSHint and ESLint and since that conversion has occurred in the version of Ember CLI we are using this option is no longer needed.

CHANGELOG

• Remove ember-cli-mocha useLintTree configuration option

[juwara0]

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