Remove `ro_data` and `rw_data` from `InterpretedModule`

[koute]

This is unnecessarily duplicated, since the Module contains this anyway as part of the program blob.

(This is an old vestigial code from back when we didn't hold a reference to a ProgramBlob.)

[aman4150]

ro_data in the InterpretedModule is padded with zeros to bring the length to ro_data_size. If I remove ro_data from InterpretedModule, implementing get_memory_slice becomes tricky.

What do you suggest here?

[koute]

@aman4150 Can't you just add an extra branch there special-casing this?

[aman4150]

Merged changes in #324