Revert addition of input placeholder rules

This commit reverts the following 5 commits:

49392e9df27b7036609f56861679e8cf9c0ea264
f9572a461a6a3baf7f151c095ab23babc4937a39
79e2c16ba5157c46ea4a129dd99420ac2f85f3f0
2691e7ab14682dc8f9e942456887df0e35804087
567af2e7d68d2bebb6428748190fd7dc5e6a4e51

The `:moz-placeholder` rule doesn't have the desired effect because any
subsequent rule with higher specificity will result in the Firefox bug
resurfacing. There is no way to ensure that Firefox doesn't change the
color of the placeholder text. Example: https://tinker.io/e34a2

The `:focus::webkit-input-placeholder` normalization is being removed
because the current Chrome / Safari on Lion OSX behaviour is allowed in
the spec, Firefox is set to implement the same behaviour, and other
browsers may follow suit for usability reasons.

Some browser differences like these - low importance and in flux - can
be allowed to evolve and settle before assessing whether or not they
need or merit normalization.