deskutils/cherrytree: update the port to version 1.2.0

Unmaintained and outdated libgtksourceviewmm3 had been replaced
with libgtksourceview4 (direct access to C API). Collaterally,
four *.lang files had been dropped from pkg-plist because those
languages are now inside the library v4 itself (were not in v3).

Reported by: portscout