Remove ignoring StrictMode violation for AutoPushFeature in FirefoxApplication#onCreate

[dnarcese]

⛔️ Blocked on https://github.com/mozilla-mobile/android-components/issues/4166

Vision statement / What / Requirements

AutoPushFeature has strict mode disk read violations. We get around this by ignoring the violation when AutoPushFeature is called (here). Once this violation is fixed, we don't have to ignore it.

Impact

Ignoring the violation would become unnecessary.

Acceptance criteria

StrictMode.allowThreadDiskReads().resetAfter is removed in FirefoxApplication#onCreate (This is the line of code).