Import and use lists:droplast/1 in v3_core/v3_kernel

Also imported lists:last/1, and removed the local definition.
Use lists:droplast/1 in orber/orber_interceptors.erl
wx/wg_gen.erl - Replace reverse(tl(reverse(L))) with lists:droplast/1
ssh/ssh_sftpd.erl - Replace reverse(tl(reverse(L))) with lists:droplast/1
mnesia/test/mnesia_frag_test.erl - Replace reverse(tl(reverse(L))) with lists:droplast/1