jjb: lava: remove untracked linux version

jjb: lava: remove untracked linux version

Linux kernel commit e39d200fa5bf5b94a0948db0dae44c1b73b84a56 was
backported to multiple Linux stable branches including linux-4.4.y.

That commit changes a tracepoint interface, thus prevents the build of
the unsupported LTTng version 2.7 on this version.

As a solution, we remove the test configuration with linux-4.4.y and
lttng stable 2.7.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>