selinux: Remove obsolete selinux_audit_data initialization.

Commit 899838b2 eliminated the need
to initialize selinux_audit_data except in the slow path, when it is
handled by slow_avc_audit().  That commit removed all other initializations
of selinux_audit_data but this one remained since the binder security
hooks are not yet upstream (posted them to linux-kernel today).

Change-Id: I735e4500cde23275686cb3208068cbf8dd7bccd7
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>