VtsHalMediaOmx: avoid std::set and std::vector of const T

These containers use std::allocator<const T>, which is an undocumented
libc++ extension to the C++ standard library. The extension was removed
in llvm.org/PR96319. Use an ordinary non-const T instead.

Bug: http://b/349681543
Test: m VtsHalMediaOmxV1_0TargetStoreTest
Flag: EXEMPT, refactor to fix build failure
Change-Id: I5b5ceed1d2618b7ce1f979242f33f6bc92df0545