Remove IE11 :-ms-input-placeholder CSS pseudo-class
Summary:
Drop the `:-ms-input-placeholder` pseudo-class which was only supported by IE10 and IE11. See
* https://web.archive.org/web/20171007012115/https://msdn.microsoft.com/library/hh772745(v=vs.85).aspx
* https://web.archive.org/web/20160316203057/https://developer.mozilla.org/en-US/docs/Web/CSS/:-ms-input-placeholder
(For comparison, Wikimedia dropped support for IE11 on their websites in 08/2024.)
Edge 12 to 18 (released 11/2018) support both the `::-ms-input-placeholder` and `::-webkit-input-placeholder` pseudo-elements. See
* https://stackoverflow.com/questions/22199047/placeholder-css-not-being-applied-in-ie-11/30827689#30827689
* https://caniuse.com/css-placeholder
Thus no need to add `::-ms-input-placeholder` stuff as there is already `::-webkit-input-placeholder` stuff.
This is a followup to rP112174b9.
Test Plan: None. Probably installing old browser versions if you don't trust documentation.
Reviewers: O1 Blessed Committers, mainframe98
Reviewed By: O1 Blessed Committers, mainframe98
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D26340