Revert "check content type in JSONRequestDeserializer"

For details of the regression this caused see
bug: #1187882

This reverts commit 2f35c942e34b6c6538a2ae2da3d01b690af3a47f.

Change-Id: Ib739d271f5caf0e8ce26c3b27a3436a20e9e311d