Revert "Split adb_main.cpp into client and daemon."

This reverts commit cf07494ac2a101c3afbe23a7d85121553f586cf7.
diff --git a/adb/usb_linux.cpp b/adb/usb_linux.cpp
index 1e5d5c8..1328830 100644
--- a/adb/usb_linux.cpp
+++ b/adb/usb_linux.cpp
@@ -310,6 +310,10 @@
     closedir(busdir);
 }
 
+void usb_cleanup()
+{
+}
+
 static int usb_bulk_write(usb_handle *h, const void *data, int len)
 {
     struct usbdevfs_urb *urb = &h->urb_out;