[zxio] Migrate zxio_close -> zxio_destroy

A side effect of this change is that this will no longer be synchronous,
which should be fine for this use case.

Change-Id: Id00307c75afca619766e02808c580a199651c465
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/1244685
Commit-Queue: Chris Suter <csuter@google.com>
Reviewed-by: Craig Stout <cstout@google.com>
1 file changed