Ensure tintColorDidChange restores the original attributes for each unique link

When called to set to an inactive state, the current implementation of `tintColorDidChange` sets all link attributes to the "inactive" state and then when called again to restore the tints, it incorrectly sets the link attributes to `.linkAttributes` even though each link could have it's own unique attributes set using `addLinkWithTextCheckingResult:attributes:`

This was originally introduced in https://github.com/mattt/TTTAttributedLabel/issues/303

Although I love the idea of setting them inactive during actionsheet displays, etc., wouldn't the expected behavior be to restore the attributes that each link originally had, rather than assuming they all shared the attributes set in the `linkAttributes` property?

For `tintColorDidChange`, I'm assuming that the only attribute we care about removing is the foreground color in order to preserve the styling of text.