emulators/i386-wine: Remove port.

This port and its pre-built binaries have not been updated lately and
emulators/wine is now providing i386 support on amd64, so remove the
i386-wine port.

Adjust CONFLICTS_INSTALL on related ports and simplify (and update both
user and developer documentation in emulators/wine).

PR: 259589
Differential Revision: https://reviews.freebsd.org/D32322