ext.echo.badge: Remove defunct CSS rule

The space after colon on this line is actually a non-breaking space
(&nbsp;), which is not allowed in this place according to CSS syntax.
Therefore all browsers ignored this rule (logging an error like
"Invalid CSS property value") and the shadow was never shown.

We could fix the rule instead, but I'm pretty sure users are used to
this by now, and in my opinion it looks better without shadow.

Bug: 53490
Change-Id: I1fd508d2059bec5cd79a6dcdce8dc9be6e6d4229
Merge "ext.echo.badge: Remove defunct CSS rule"