Remove all but one use of WeakPtrFactory::DetachFromThread.

net/proxy/dhcp_proxy_script_fetcher_win.cc

Index: net/proxy/dhcp_proxy_script_fetcher_win.cc
diff --git a/net/proxy/dhcp_proxy_script_fetcher_win.cc b/net/proxy/dhcp_proxy_script_fetcher_win.cc
index 64f51179806cc46d4cebac560cb05522bc568cc4..9e34f5122e46752ac97c9ab55a431488d182ac22 100644
--- a/net/proxy/dhcp_proxy_script_fetcher_win.cc
+++ b/net/proxy/dhcp_proxy_script_fetcher_win.cc
@@ -47,11 +47,6 @@ DhcpProxyScriptFetcherWin::DhcpProxyScriptFetcherWin(
 DhcpProxyScriptFetcherWin::~DhcpProxyScriptFetcherWin() {
   // Count as user-initiated if we are not yet in STATE_DONE.
   Cancel();
-
-  // The WeakPtr we passed to the worker thread may be destroyed on the
-  // worker thread.  This detaches any outstanding WeakPtr state from
-  // the current thread.
-  base::SupportsWeakPtr<DhcpProxyScriptFetcherWin>::DetachFromThread();
 }
 
 int DhcpProxyScriptFetcherWin::Fetch(base::string16* utf16_text,