xbps_chroot_handler: do not umount, leave this to the signal handler of xbps-src.

xbps-src/shutils/chroot.sh.in

@@ -222,13 +222,6 @@ _mount()
 	return $?
 }
 
-_umount()
-{
-	MASTERDIR="${XBPS_MASTERDIR}" ${sudo_cmd} \
-		@@XBPS_INSTALL_LIBEXECDIR@@/xbps-src-chroot-helper umount
-	return $?
-}
-
 xbps_chroot_handler()
 {
 	local action="$1"
@@ -277,7 +270,6 @@ xbps_chroot_handler()
 	fi
 
 	msg_normal "Exiting from the chroot on $XBPS_MASTERDIR."
-	_umount
 
 	return $?
 }