Revert "Merge pull request #4519 from guardian/svg-sprite-optimisation-u...

...rlencoded"

This reverts commit 8b2168e4086d3c6d77c2c9052efbce18d92d2cfa, reversing
changes made to 3103fd196b0e84e17bde4aa312f399d86b65f0b9.

Fixes #4572