Simplify libdexfile external api.

Bug: 123517037
Test: m test-art-host-gtest
Test: libunwindstack_unit_test
Test: simpleperf_unit_test --gtest_filter=*dex*
Change-Id: I1bd9a6849ad79d9ddd0a0dfb93ea7c7d2311bf49
7 files changed