Get rid of --text-primary-color which is deprecated

[mercmobily]

In this file you are still using --text-primary-color:

https://github.com/PolymerElements/paper-fab/blob/8dcf4f13cf9793d9ef9b819d908e77802a550da8/paper-fab.html#L68

This stile is now deprecated:

https://github.com/PolymerElements/paper-styles/blob/master/default-theme.html#L64-L68

[keanulee]

Should replace it with --dark-theme-text-color to keep the default value consistent. This would be breaking API change for paper-fab though (since --text-primary-color will be no longer available), so best to leave it until the next breaking release.

[mercmobily]

I frankly think that using --dark-theme-text-color has the potential of not being so good, since it feels to me like it's only a variable meant to facilitate the setting of the "real" paper variables ( --primary-color --light-primary-color, --dark-primary-color, etc). The only other element using a --dark-theme variable is the paper-toolbar. In my own CSS I don't even set the --dark-theme or light-theme variables.