Erroneous `transition-delay` values in genericons.css

[SergeyBiryukov]

Background: #43195 in WordPress Core Trac.

Per https://developer.mozilla.org/en-US/docs/Web/CSS/time:

Although unitless zero is allowed for <length>s, it's invalid for <time>s.

So we could drop transition-delay on these two lines since the default is 0s anyway:

-moz-transition: color .1s ease-in 0;
-webkit-transition: color .1s ease-in 0;

Should be:

-moz-transition: color .1s ease-in;
-webkit-transition: color .1s ease-in;