Revert "Merge pull request #4381 from guardian/svg-sprite-optimisation"

This reverts commit 071544d6f5bf607f0195ddf277d726533e6be148, reversing
changes made to 877792e142c7a2db3ef70396679cd7dde42bd92d.
Merge pull request #4382 from guardian/revert-pull-request-4381

Revert "Merge pull request #4381 from guardian/svg-sprite-optimisation"