Replace method_type with AidlMethod

As usual, we're leaving most of the same members in place and public. However,
we have removed the linked list pointer and switched to std::vector for lists
of methods.

Change-Id: Id0aa55340e2c56bfa1001c6c8a8343bb4815d38e
Test: unit tests
Bug: 24410295
Signed-off-by: Casey Dahlin <sadmac@google.com>
6 files changed