libcutils: Stop checking the uid of netlink messages

This is a partial revert of
https://android-review.googlesource.com/c/platform/system/core/+/528619.
The uid-check was done before
https://patchwork.kernel.org/patch/1525551/ was available, and thus is
now unnecessary to perform such check, since we can just rely on the
kernel patch now.

Bug: 71632076
Test: aosp_sailfish-userdebug still works

Change-Id: I1d1319b774483d1714ecb4dd838a20e055acc2a3