Rip out one of the features I added for the driver-include-management.

We don't actually need a separate flag for non-sysrooted paths as the
driver has to manage the sysroot anyways. The driver is not infrequently
adding paths to the header search based on their existence on the
filesystem. For that, it has to add the sysroot anyways, we should pass
it on down to CC1 already joined. More importantly, the driver cannot in
all cases distinguish between sysrooted paths and paths that are
relative to the Clang binary's installation directory. Essentially, we
always need to ignore the system root for these internal header search
options. It turns out in most of the places we were already providing
the system root in the driver, and then another one in CC1 so this fixes
several bugs.

llvm-svn: 143917