shill: cellular: Remove mobile_provider.h includes. Cellular code no longer depends on mobile-provider. Remove header includes so that we can drop the dependence. BUG=chromium:371630 TEST=emerge-peppy platform2. Change-Id: I9b8f433744b6149f59cb6e192eb446a220cbbea3 Reviewed-on: https://chromium-review.googlesource.com/201170 Reviewed-by: Thieu Le <thieule@chromium.org> Commit-Queue: Prathmesh Prabhu <pprabhu@chromium.org> Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>