Revert "Turn off adb on user builds."

This reverts commit 8ad4bb16a0.

Bug: 184103246
Test: forrest test build
Change-Id: I9111ae2d6150dfed86c785e6db205c64e4c8d5e0

tools/post_process_props.py

@@ -38,11 +38,6 @@ def mangle_build_prop(prop_list):
       else:
         val = val + ",adb"
       prop_list.put("persist.sys.usb.config", val)
-  # UsbDeviceManager expects a value here.  If it doesn't get it, it will
-  # default to "adb". That might not the right policy there, but it's better
-  # to be explicit.
-  if not prop_list.get_value("persist.sys.usb.config"):
-    prop_list.put("persist.sys.usb.config", "none")
 
 def validate_grf_props(prop_list, sdk_version):
   """Validate GRF properties if exist.