libstagefright_aidl_bufferpool2: avoid list<const T>

A container of const T uses std::allocator<const T>, which was an
undocumented libc++ extension that has been removed.

See https://github.com/llvm/llvm-project/pull/96319.

Bug: 349681543
Test: m libstagefright_aidl_bufferpool2
Change-Id: I6491377d6275c5d18cd91b40184d6f05cff7cb9a