Remove vendor-prefixed -moz-transition CSS syntax
Summary:
`-moz-transition` syntax was only supported from Firefox 4 to Firefox 15 according to https://web.archive.org/web/20130827073113/https://developer.mozilla.org/en-US/docs/Web/CSS/transition.
Per https://web.archive.org/web/20130827073113/https://developer.mozilla.org/en-US/docs/Web/CSS/transition and https://caniuse.com/mdn-css_properties_transition, standard `transition` has been supported since Firefox 16 released 08/2012.
Per https://developer.mozilla.org/en-US/docs/Web/CSS/Mozilla_Extensions, `-moz-transition` is not supported anymore and https://developer.mozilla.org/en-US/docs/Web/CSS/transition should be used.
Test Plan: Read CSS docs. Probably install ancient browser versions if you don't trust documentation. Try https://jigsaw.w3.org/css-validator/ and don't spot issues.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D25971