vbe grew PanelID support in xserver 1.4; since we now require 1.6 we can
remove the test.  Which is good, because it appears to have been broken
by the scrnIndex->pScrn conversion, as vbe.h doesn't include xf86str.h
so ScrnInfoPtr was never defined and the test failed.

Signed-off-by: Adam Jackson <ajax@redhat.com>