Disable bogus code for finding and linking against ncurses.
For some very old reason lost in the dawn of time, HHVM imported the
CMake file of Readline from KDE, which had an ncurses dependency. Remove it
from everywhere.

Sync with Debian patch 08_disable_libncurses.patch from 2.4.1-1.
Merge pull request #2087 from Jo-Con-El/debian-08_disable_libncurses

Disable bogus code for finding and linking against ncurses.