Unnecessary vendor prefixes should be removed

[helenyhou]

Some vendor prefixes for some or all properties aren't needed anymore, such as -khtml-* and some -moz-* and -webkit-*. Research and testing needs to be done, especially regarding Safari on iOS.

Some fairly certain ones:

• all -khtml-*
• -moz/webkit/o-border-radius
• -moz/webkit/o-text-shadow
• ...

Ones that have to stay:

• *-transform
• ...

get rid of -khtml

We need this to make wp-admin.css a bit smaller, see #18314.

Border-radius:
​https://developer.mozilla.org/en/CSS/border-radius#Browser_compatibility

-webkit is still needed for mobile browsers.

remove vendor prefix for text-shadow

Replying to ocean90:

-webkit is still needed for mobile browsers.

Thought we were removing all -moz-border-radius too. Not needed since Gecko 1.8.

In [18726]:

Remove unnecessary vendor prefixes, props ocean90, see #18700

Removes the same vendor prefixes in the RTL stylesheet.

In [18962]:

Remove unnecessary vendor prefixes from wp-admin-rtl.css, props ryanimel, see #18700

Get rid of -khtml-* and -moz-border-radius in remaining files.

Attached patch should likely get rid of all remaining -khtml-* rules in .dev.css files. Some still remain in non-dev files (like TinyMCE), though. Also twentyten/eleven I think. It also gets rid of -moz-border-radius in other CSS files that were missed.

Per [18726] and [18962], looks good.

In [19203]:

Remove old vendor prefixes. props andrewryno, ocean90, fixes #18700.