CA-248658: Revert "CA-247700: Don't GC VBDs that are currently attached"
CA-248658: Revert "CA-247700: Don't GC VBDs that are currently attached"

This reverts commit 126a68426be1e86383dd03d53cd50b6c853c8648, because we
suspect that it introduced a regression.

Signed-off-by: Rob Hoes <8783b3376fb07d39edffc8d7da68a6de3874a7e6@citrix.com>

srowe/xen-api,euanh/xen-api,euanh/xen-api,euanh/xen-api,srowe/xen-api,srowe/xen-api,euanh/xen-api,Frezzle/xen-api,Frezzle/xen-api,srowe/xen-api,srowe/xen-api,Frezzle/xen-api,euanh/xen-api,euanh/xen-api,Frezzle/xen-api,Frezzle/xen-api