[adb] Followup CL to clean up adb_auth_host.cpp

Get rid of unused includes + replace a fixed-size buffer with an
std::string

(cherry-pick of ef21b5556ddd621665107008e2acc3f4843a565d.)

Change-Id: I4f9927b900a79a012b5d52908b9d22ac3d2a401c
1 file changed