Debugger: Remove the "Attempt quick start option"

This was GDB-only. It complicates the startup mechanism including breaking
certain setups (e.g. users manually controlling "set auto-solib-add" in
their .gdbinit) without providing too much benefit (anymore).

Part of the potential debugger startup time improvements that were
possibly gained by the feature are nowadays available by using a
release build *without* debug info, as one of the original reasons
to not use that (making Qt type introspection hard/impossible)
is largely gone with 4.2+.

Change-Id: Iffb34e0035f39ad74b24bf025749b546f25a489b
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/gdb/gdbengine.h

@@ -407,10 +407,6 @@ protected:
     void requestDebugInformation(const DebugInfoTask &task);
     DebugInfoTaskHandler *m_debugInfoTaskHandler;
 
-    // Indicates whether we had at least one full attempt to load
-    // debug information.
-    bool attemptQuickStart() const;
-    bool m_fullStartDone;
     bool m_systemDumpersLoaded;
 
     static QString msgGdbStopFailed(const QString &why);