Revert "Fixed proxy error on file attachment [ENSEMBL-3488]"

The fix has now been included in ensembl_webcode on the release/77 branch, so removing from eg-web-common master branch.  Leaving fix in the eg/release/23 branch as there is no corresponding fix in ensembl-webcode's release/76 branch.

This reverts commit cf4214f27db2628ae55c84e1a1c2d5e768b75d01.