audio/hts_engine-API: fix pkg-plist

pkg-plist hardcoded a framework-managed line:

@dir share/licenses/hts_engine-API-1.10

share/licenses/<pkg>/ is created automatically by the LICENSE
framework and must never be in pkg-plist.

Putting that line causes a packaging failure when DISABLE_LICENSES=yes
is set:
pkg-static: Unable to access .../share/licenses/hts_engine-API-1.10/: No such file or directory