Only try to remove a GC root if it's actually used
Only try to remove a GC root if it's actually used

These are initialized with cUndef. We already guard the cases for adding
them so we don't add cUndef, so we should also guard this case when
trying to remove it.

dblock/rubinius,jemc/rubinius,ngpestelos/rubinius,kachick/rubinius,heftig/rubinius,dblock/rubinius,kachick/rubinius,pH14/rubinius,heftig/rubinius,ruipserra/rubinius,pH14/rubinius,benlovell/rubinius,dblock/rubinius,ruipserra/rubinius,sferik/rubinius,heftig/rubinius,ruipserra/rubinius,Wirachmat/rubinius,heftig/rubinius,heftig/rubinius,heftig/rubinius,pH14/rubinius,dblock/rubinius,pH14/rubinius,mlarraz/rubinius,jemc/rubinius,benlovell/rubinius,jemc/rubinius,ngpestelos/rubinius,digitalextremist/rubinius,mlarraz/rubinius,sferik/rubinius,mlarraz/rubinius,benlovell/rubinius,dblock/rubinius,kachick/rubinius,heftig/rubinius,sferik/rubinius,kachick/rubinius,benlovell/rubinius,pH14/rubinius,jemc/rubinius,mlarraz/rubinius,kachick/rubinius,digitalextremist/rubinius,kachick/rubinius,Wirachmat/rubinius,sferik/rubinius,jemc/rubinius,jsyeo/rubinius,sferik/rubinius,jemc/rubinius,pH14/rubinius,ngpestelos/rubinius,jsyeo/rubinius,ruipserra/rubinius,ngpestelos/rubinius,dblock/rubinius,Wirachmat/rubinius,ngpestelos/rubinius,Azizou/rubinius,Azizou/rubinius,ngpestelos/rubinius,benlovell/rubinius,kachick/rubinius,mlarraz/rubinius,benlovell/rubinius,dblock/rubinius,Azizou/rubinius,Azizou/rubinius,sferik/rubinius,mlarraz/rubinius,Azizou/rubinius,Azizou/rubinius,benlovell/rubinius,digitalextremist/rubinius,Wirachmat/rubinius,kachick/rubinius,digitalextremist/rubinius,ruipserra/rubinius,digitalextremist/rubinius,ngpestelos/rubinius,sferik/rubinius,digitalextremist/rubinius,jsyeo/rubinius,digitalextremist/rubinius,jsyeo/rubinius,mlarraz/rubinius,Wirachmat/rubinius,jsyeo/rubinius,jsyeo/rubinius,Wirachmat/rubinius,jsyeo/rubinius,Wirachmat/rubinius,pH14/rubinius,ruipserra/rubinius,ruipserra/rubinius,jemc/rubinius,Azizou/rubinius