Partially revert "stretch triage"

This (partially) reverts commit b7e957b2.

CVE-2018-15126 affects the libvncserver codebase on 0.9.11 but the
patchset to be applied is refactoring and introducing two new symbols to
fix the issue.

Similar conclusion reached by SuSE triage at
https://bugzilla.novell.com/show_bug.cgi?id=1120114#c3