[fastboot+init] avoid std::allocator<const T>

std::vector<const T> uses 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 fuzzy_fastboot CtsInitTestCases
Test: m MODULES-IN-system-core
Flag: EXEMPT, refactor to fix build failure
Change-Id: Ia98a2f090e87541fd35a89bd75bf9638bc7dc711