qemu: Remove qemu_hotplugpriv.h and qemuDomainRemoveDeviceWaitTime

qemu: Remove qemu_hotplugpriv.h and qemuDomainRemoveDeviceWaitTime

qemu_hotplugpriv.h is a header file created to share a global variable
called 'qemuDomainRemoveDeviceWaitTime', declared in qemu_hotplug.c,
to other files that would want to change the timeout value
(currently, only tests/qemuhotplugtest.c).

Previous patch deprecated the variable, using qemu_driver->unplugTimeout
to set the timeout instead. This means that the header file is now
unused, and can be safely discarded.

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>