ANDROID: binder: remove extra declaration left after backport

When backporting commit 1a7c3d9b ("binder: create
userspace-to-binder-buffer copy function"), an extra "int target_fd;"
was left in the code. This resulted in the possibility of accessing
an uninitialized variable which was flagged by gcc.

Bug: 67668716
Change-Id: I787ed89579e9d40e8530d79be67cc663ec755e54
Signed-off-by: Todd Kjos <tkjos@google.com>