Remove "//apex_available:platform"

There is no one in platform that refers to
dnsresolver_aidl_interface-java, so dnsresolver_aidl_interface-java
doesn't need to be available for platform.

Bug: 184015724
Test: m & atest
Change-Id: I59a7440d7a44a90ac92d54419728f256d4174f76
Ignore-AOSP-First: Some of related commits need to merge into AOSP
first, otherwise there will be a merge conflict in internal branches.