Log Message:
wm/leftwm: Fix broken build

See, \ 
http://www.ki.nu/pkgsrc/reports/current/NetBSD-9.0/20221007.2334/leftwm-0.4.0/build.log
Caused by regenerated 'Cargo.lock'.
Fetch the correct versions of dependencies.

While here, add a conflict with 'lefthk'.
The daemon is built-in the WM and the standalone package is only
intended to be used with other WMs.