Remove unused boost/process.hpp include from gbmcweb chassis.cc and systems.cc.

These two files include `<boost/process.hpp>` but do not use Boost.Process
(they call `SubprocessUtilsBase::childProcessRun`). Since Boost 1.86,
`<boost/process.hpp>` is Boost.Process v2, which is not header-only anymore.
Its error categories are then undefined at link time, so `webserver_main`
and the chassis and system tests fail to link with Boost 1.92. Removing the
include fixes this. This builds with the current Boost 1.83 and with Boost 1.92.

Google-Bug-Id:567853120
PiperOrigin-RevId: 997286821
Change-Id: I62f4f6ab2d5c57d0283d09f00ca625061eae1b18