Remove No Longer Used SVGs

* Delete unused icons (including a few duplicate icons that had two different names!)
* Optimise recently added SVGs (comment recommendation arrow, pagination arrows)
* Move some icons from global folder to content folder
* Move some (soon to be deprecated arrow) icons from global folder to commercial folder

More icons can be removed, but are attached to more substantial changes (i.e. JavaScript and Scala files that can also be removed). Will do these removals in separate PRs.

/cc @phamann