The writembs macro was ported from C++, which attempted to detect when a NULL
termcap was used. However we have never gotten a bug report from this. Bravely
remove it.
Per code review, we think that tparm does nothing when there are no parameters,
and it is safe to remove it, even though this is a break from C++. This
simplifies some code.
Either add rust wrappers for C++ functions called via ffi or port some pure code
from C++ to rust to provide support for the upcoming `env_dispatch` rewrite.
