process interruption improvements

rely on the inferior's pid being available. consequently, remove the
bizarre findChild stuff.

src/plugins/debugger/procinterrupt.h

@@ -36,7 +36,6 @@ namespace Debugger {
 namespace Internal {
 
 bool interruptProcess(int pID);
-bool interruptChildProcess(Q_PID parentPID);
 
 } // Internal
 } // GdbDebugger