Fix encoder spot light angle conversion

Light inner/outer angles are [already in radians](https://github.com/blackberry/GamePlay/blob/4067ce019dccb23a38a6b186b77f43c6fe986e5c/tools/encoder/src/FBXSceneEncoder.cpp#L822), no need to convert again when writing out.  This fixes light nodes having bogus inner and outer angles when loading from a `.gpb` that was generated from a `.fbx`.

This is only a step in the right direction though; when exporting a light from, say, blender, the inner and outer angles are written into the file, however `gameplay-encoder` only reads in the outer angle (called `falloffAngle`) and then computes an estimated inner angle.  Should I submit a PR to read in the true inner and outer angles from the `.fbx`?

An example `.fbx` with the inner and outer angles present is [here](https://gist.github.com/staticfloat/7798794).  I am specifically referring to the `spot` node.