net: Remove the get current NAPI context API

rmnet_data no longer uses the API get_current_napi_context()
since it now relies on the device NAPI struct for GRO.
There are no other users of this API.

Change-Id: Ibc41c0a5cc3b83b02e834c413fa61273321e93ca
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>