Remove android.net.rtp from preloaded classes

These cause /dev/urandom to be opened as CLO_EXEC and test
android.security.cts.FileDescriptorTest#testCLOEXEC to fail.

Also added to denylist except for AudioCodec that is pulled from
somewhere.

Bug: 174053659
Test: atest ./cts/tests/tests/security/src/android/security/cts/FileDescriptorTest.java
Change-Id: I1d83a1127ef3a0dce7ba0afa7549d2e4ec8ba453