Gtk2HsStore.c: Remove invalid assertions.

See the thread I began on 2014-01-24 entitled "Error when adding nodes to a tree store in response to testExpandRow". The (invalid) assertion that was causing the immediate problem was removed and a new release was done. I installed that and more invalid assertions turned up that caused incorrect behavior similar, but not identical to the first issue (in this case, a node would expand, but not all its children would be visible; contracting and expanding again would work, because the grandchildren had gotten created as a result of the first expansion request and it is the creation of the grandchildren that creates the situation that triggers the bogus assertions; see the email thread). I found the documentation here on github that explains how to build and install from source with cabal-meta (thank you for the good documentation), deleted the bad assertions, and installed on my system. My application now behaves correctly.