ftl: delegate SmallVector<const T> to std::vector<T>

An STL container of const T uses std::allocator<const T>, which was
an undocumented libc++ extension that has been removed. See
llvm.org/PR96319.

Bug: http://b/349681543
Test: ftl_test
Change-Id: Ic5ef8b80231bd58b77e5ca0ee48f263b03973a3f
1 file changed