Revert "Add support for svg in .list-style-image"

Revert "Add support for svg in .list-style-image"

The generated CSS is invalid, as you can't have multiple
list-style-images (unlike background-images). Browsers
either ignore the invalid properties with linear-gradient
and use non-embedded PNG fallback (Chrome, Firefox, modern
IE), or accept the properties but ignore everything after
the comma, using the fully transparent gradient (Opera).

This reverts commit 502fffe3bf2cb6a8fccb8059436a038e21153596.

Change-Id: I87f8142b5e718f96ca8ee74578224b4db7dedce9