Use std::list to store Behavior objects

There's a bug about behavior being null. It's not clear how it gets
there, but before this CL, there was a custom implementation of linked
list to store the behaviours. Instead of implementing a
custom linked list, let's switch over to std::list to remove the
possibility of this bug.

Bug: 238626341
Test: atest libinput_tests inputflinger_tests KeyCharacterMapTest
Change-Id: I98e20de7d40b74e4af085cdafb68f867e6ebfe19