We currently have some CSS rules in `common/base/rtl.scss` that were added to workaround shortcomings of the R2 gem that we used to use to generate versions of our CSS that are suitable for RTL layouts. Those workarounds are mostly duplicates of existing rules with the only difference being that they're flipped to suit RTL layouts (e.g. `padding-left` is changed to `padding-right` and vice versa).
However, we've recently replaced R2 with `rtlcss` which doesn't have those shortcomings of R2 (see f94951147e) which means those workarounds/duplicate rules need to be removed because they're getting flipped by `rltcss`, essentially reverting them to their original LTR version and causing issues with RTL layouts.
This commit removes those workarounds that are no longer needed, and cleans up the the file that contains our RTL-specific CSS.
Meta topic: https://meta.discourse.org/t/avatar-in-rtl-website-in-wrong-place/264676?u=osama.
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