Remove build/libs

There's only a single library, libhost, and it's only used by acp and
atree in build/tools, move it there.

Bug: 28001743
Change-Id: Ie404d2793710de4e265a6fa95d462c32d4042623

diff --git a/libs/host/Android.bp b/tools/libhost/Android.bp
similarity index 100%
rename from libs/host/Android.bp
rename to tools/libhost/Android.bp

diff --git a/libs/host/CopyFile.c b/tools/libhost/CopyFile.c
similarity index 100%
rename from libs/host/CopyFile.c
rename to tools/libhost/CopyFile.c

diff --git a/libs/host/include/host/CopyFile.h b/tools/libhost/include/host/CopyFile.h
similarity index 100%
rename from libs/host/include/host/CopyFile.h
rename to tools/libhost/include/host/CopyFile.h