Revert "fix a leak of file descriptors"
This reverts commit
791c0e2daf69cf0dfd132b021f08252f0ad9324c.
The user of libtbm have to control state of "fd" by himself. So libtbm shouldn't save fd which received by tbm_bo_import_fd()
Change-Id: Ic62d6a6363762691bfd06bab913949e907ee660a