Revert "Make transition to "postinstall" domain explicit."

This reverts commit 20e3960e245f6dfa57fa5c9124b0fd33e679f723.

Bug: 28008031

Change-Id: If5fcb949dee91779bea465793ec2b333d27a704e
diff --git a/p2p_manager.cc b/p2p_manager.cc
index bcfe156..127e5ff 100644
--- a/p2p_manager.cc
+++ b/p2p_manager.cc
@@ -396,10 +396,7 @@
 
     // We expect to run just "p2p-client" and find it in the path.
     child_pid_ = Subprocess::Get().ExecFlags(
-        cmd,
-        Subprocess::kSearchPath,
-        {},
-        nullptr,
+        cmd, Subprocess::kSearchPath, {},
         Bind(&LookupData::OnLookupDone, base::Unretained(this)));
 
     if (!child_pid_) {