travis: remove libedit-dev dependency in LLVM 6.0 targets

In LLVM <6.0 we added explicitly libedit-dev, as it was required to
satisfy apt dependencies.

In LLVM 6.0, this is not required anymore, so let's remove it.

CC: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
1 file changed