Remove -detachdb and stop's detach argument.

As the only BDB database left is the wallet, and it is always
detached.

Also remove IsChainFile() predicate and related chainfile-specific
logic.

src/init.cpp

@@ -265,7 +265,6 @@ std::string HelpMessage()
         "  -upnp                  " + _("Use UPnP to map the listening port (default: 0)") + "\n" +
 #endif
 #endif
-        "  -detachdb              " + _("Detach block and address databases. Increases shutdown time (default: 0)") + "\n" +
         "  -paytxfee=<amt>        " + _("Fee per KB to add to transactions you send") + "\n" +
 #ifdef QT_GUI
         "  -server                " + _("Accept command line and JSON-RPC commands") + "\n" +
@@ -408,8 +407,6 @@ bool AppInit2()
     else
         fDebugNet = GetBoolArg("-debugnet");
 
-    bitdb.SetDetach(GetBoolArg("-detachdb", false));
-
 #if !defined(WIN32) && !defined(QT_GUI)
     fDaemon = GetBoolArg("-daemon");
 #else