travis: Remove now-unnecssary items from apt-mark hold lists.
travis: Remove now-unnecssary items from apt-mark hold lists.

This seems to have been causing the travis production suite to fail.
It's a direct consequence of removing travis' giant library of apt
sources.list files; now that those are gone, there aren't copies of
all these extra packages available anyway.

dhcrzf/zulip,timabbott/zulip,hackerkid/zulip,zulip/zulip,punchagan/zulip,tommyip/zulip,synicalsyntax/zulip,zulip/zulip,shubhamdhama/zulip,hackerkid/zulip,shubhamdhama/zulip,rishig/zulip,dhcrzf/zulip,tommyip/zulip,synicalsyntax/zulip,dhcrzf/zulip,showell/zulip,dhcrzf/zulip,showell/zulip,eeshangarg/zulip,dhcrzf/zulip,punchagan/zulip,shubhamdhama/zulip,jackrzhang/zulip,brainwane/zulip,rht/zulip,andersk/zulip,mahim97/zulip,synicalsyntax/zulip,kou/zulip,eeshangarg/zulip,eeshangarg/zulip,jackrzhang/zulip,andersk/zulip,rishig/zulip,shubhamdhama/zulip,rishig/zulip,shubhamdhama/zulip,andersk/zulip,jackrzhang/zulip,rishig/zulip,tommyip/zulip,brainwane/zulip,eeshangarg/zulip,kou/zulip,andersk/zulip,synicalsyntax/zulip,hackerkid/zulip,kou/zulip,punchagan/zulip,dhcrzf/zulip,showell/zulip,mahim97/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,rht/zulip,rishig/zulip,hackerkid/zulip,timabbott/zulip,shubhamdhama/zulip,eeshangarg/zulip,hackerkid/zulip,showell/zulip,kou/zulip,showell/zulip,timabbott/zulip,brainwane/zulip,hackerkid/zulip,mahim97/zulip,mahim97/zulip,punchagan/zulip,jackrzhang/zulip,showell/zulip,zulip/zulip,rishig/zulip,synicalsyntax/zulip,dhcrzf/zulip,jackrzhang/zulip,andersk/zulip,rht/zulip,mahim97/zulip,synicalsyntax/zulip,jackrzhang/zulip,brainwane/zulip,rht/zulip,zulip/zulip,tommyip/zulip,zulip/zulip,jackrzhang/zulip,tommyip/zulip,kou/zulip,showell/zulip,punchagan/zulip,rht/zulip,punchagan/zulip,brainwane/zulip,brainwane/zulip,punchagan/zulip,timabbott/zulip,hackerkid/zulip,mahim97/zulip,timabbott/zulip,timabbott/zulip,rht/zulip,zulip/zulip,zulip/zulip,rht/zulip,rishig/zulip,shubhamdhama/zulip,tommyip/zulip,brainwane/zulip,timabbott/zulip,andersk/zulip,tommyip/zulip,synicalsyntax/zulip,eeshangarg/zulip,kou/zulip