bind/objc: fix compile warning
bind/objc: fix compile warning

An extra struct initializer was left over from an earlier version
of the direct call conversion. Remove it.

Change-Id: I19c3eb3be7bf78378af47ea182931b0c24cdd34d
Reviewed-on: https://go-review.googlesource.com/21104
Reviewed-by: David Crawshaw <a2f0bf29257797dd66800b4fbb9945c3e216c004@golang.org>

golang/mobile,golang/mobile,golang/mobile,golang/mobile