Disable format determination based on path extension

Replaces controller/action-specific changes made in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/19876, https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/19937, https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20023, https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/19907, https://gitlab.com/gitlab-org/gitlab-ce/commit/1292b99b742fd83438b011d3082662d354b3330e.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/54278 by removing JSON-specific exception from Projects::BlobController#set_request_format? (and the entire method with it 😃)