Always encode struct lists as INLINE_COMPOSITE per new canonicalization rules.

Extended discussion:
https://groups.google.com/d/msg/capnproto/lRlWBOglQv4/8-Qo96AcZQIJ
Remove hacks that support List(Bool) -> List(struct) upgrades (no longer allowed).

Extended discussion:
https://groups.google.com/d/msg/capnproto/lRlWBOglQv4/8-Qo96AcZQIJ
Merge branch 'master' of github.com:kentonv/capnproto

Conflicts:
	c++/src/capnp/generated-header-support.h