Simplify I/O types. Remove unused/proxy chips and gate.

[pmikolajczyk41]

1. Remove point_double chip and gate - they are not used. Doubling is done within scalar_multiply gate.
2. Remove chips for checking whether projective/affine point is on curve. They only proxied input to the gate. Now we are using gate directly.
3. Remove wrappers for input/output values in curve chips. They usually wrapped a single value into a named field - abandoning them results in a more concise code.

[guspiel]

LGTM