ANDROID: fix redefinition error for restricted vendor hooks

Because of the multi-inclusion oddities of tracepoints, the
multi-inclusion protection in vendor_hooks.h caused issues
if more than 1 vendor hook header file with restricted vendor
hooks defined were included with "CREATE_TRACE_POINTS"
defined (redefinition of symbol errors).

The problem is fixed by removing the multiple-inclusion
protection as is done for regular tracepoints.

Fixes: 5965ee66 ("ANDROID: add support for vendor hooks")
Bug: 163076069
Signed-off-by: Todd Kjos <tkjos@google.com>
Change-Id: Ic177db1693a6a2db58f08917e9115c7e6c2971b6