Removing deprecated LESS `.background-size()` mixin calls.
Also
- simplifying code, where second (height) value is automatically set
to `auto` when only one value is set and
- removing stylelint rule.
Bug: T219956
Change-Id: I643c66b3067ba77726d76cbebf7550781e18aa5d
This exposes two broken tests:
* #setCount (Eastern Arabic numerals)
* clicking on the product of createBanner() should trigger a custom event
that were previously passing due to buggy assertions.
Change-Id: If18ad1ff9363fff65d3e347c01ce4bc0669b2a0e