build: Remove "pvh_boot" feature flag

This feature is stable and there is no need for this to be behind a
flag. This will also reduce the time needed to run the integration test
as we will not be running them all again under the flag.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

Cargo.toml

@@ -40,7 +40,6 @@ acpi = ["vmm/acpi"]
 pci = ["vmm/pci_support"]
 mmio = ["vmm/mmio_support"]
 cmos = ["vmm/cmos"]
-pvh_boot = ["vmm/pvh_boot"]
 
 # Integration tests require a special environment to run in
 integration_tests = []