NDK: Report RGBA_F16 as appropriate

Bug: 135133301
Test: Id904c8cb4b22505635744ab271a639ace24ddbab

I3c17faf174b109b7c31c2eb5d1249bc881923b10 adds a new AndroidBitmapFormat
which corresponds to Bitmap.Config.RGBA_F16. Report it if that is the
format of the Bitmap.

Remove unnecessary SkASSERTs, which are turned off for Android builds.

Change-Id: Id05497d0bcbfa5ccb3109e2819eecbbf84d35149