fix(button): exclude solid from getting added to the button in the class
fix(button): exclude solid from getting added to the button in the class

This prevents `button-solid-secondary` from being added when it should
just be `button-secondary`.

references #6202

jhlee8804/ionic,jhlee8804/ionic,AbraaoAlves/ionic,alan-agius4/ionic,jarrodkoch/ionic,driftyco/ionic,alan-agius4/ionic,jarrodkoch/ionic,janglednerves/ionic,AbraaoAlves/ionic,joshesp/ionic,alan-agius4/ionic,janglednerves/ionic,TillaTheHun0/ionic,cambronjay/ionic,dennybiasiolli/ionic,driftyco/ionic,AbraaoAlves/ionic,janglednerves/ionic,TillaTheHun0/ionic,jarrodkoch/ionic,jarrodkoch/ionic,alan-agius4/ionic,cambronjay/ionic,joshesp/ionic,manucorporat/ionic,dennybiasiolli/ionic,joshesp/ionic,manucorporat/ionic,jarrodkoch/ionic,dennybiasiolli/ionic,janglednerves/ionic,AbraaoAlves/ionic,jhlee8804/ionic,dennybiasiolli/ionic,joshesp/ionic,jhlee8804/ionic,driftyco/ionic,manucorporat/ionic,cambronjay/ionic,dennybiasiolli/ionic,driftyco/ionic,manucorporat/ionic,alan-agius4/ionic,alan-agius4/ionic,driftyco/ionic,jhlee8804/ionic,TillaTheHun0/ionic,cambronjay/ionic,cambronjay/ionic,manucorporat/ionic,TillaTheHun0/ionic,brianespinosa/ionic2-sass,janglednerves/ionic,AbraaoAlves/ionic