Remove message and comment autocompletion

The autocompletion of messages and comments doesn't properly deal with
line breaks in the current implementation. Disable those for now.
6 jobs for autocomplete
Status Name Job ID Coverage
canceled debian_stretch_x86_64_deb #27937
debian stretch x86_64

canceled osx_10.11_x86_64_dmg #27939
osx v10.11 dmg

canceled osx_10.8_x86_64_dmg #27940
osx v10.8 dmg

canceled raspbian_stretch_armv7l_deb #27942
raspbian arm stretch

canceled ubuntu_16.04_x86_64_deb #27938
ubuntu v16.04 x86_64

canceled windows_i386_innosetup #27941
windows i386