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>

tests/integration.rs

@@ -1052,7 +1052,7 @@ mod tests {
         });
     }
 
-    #[cfg_attr(feature = "pvh_boot", test)]
+    #[test]
     fn test_pvh_boot() {
         test_block!(tb, "", {
             let mut clear = ClearDiskConfig::new();