[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 049ebb810f466d916ec9e73cdf28624b57a8c25d.)

Change-Id: I4f9927b900a79a012b5d52908b9d22ac3d2a401c
1 file changed