Get rid of IDevice::signalOperation()

Rely on ProcessInterface::sendControlSignal() instead.

It looks like in some cases we are using DeviceProcessSignalOperation for killing a process without having associated QtcProcess instance:

SshDeviceProcessList::doKillProcess()
LocalProcessList::doKillProcess()

It kills the selected process using processId.

RemoteLinuxKillAppService::doDeploy()

It kills the process using path.

So we should still be able to do this without having associated process instance.

In addition we currently have 2 usages of DeviceProcessSignalOperation for interrupting running process:

CdbEngine::doInterruptInferior()
GdbEngine::interruptInferior()

In this case most probably they may be substituted with a call to associated QtcProcess::interrupt().

Moreover, the:

Debugger::Internal::interruptProcess()

used on linux for local and remote, implements its own interrupt by calling kill with SIG_INT - this should be most probably replaced by a call to QtcProcess::interrupt().

We should also probably implement QtcProcess::interrupt() by sending SIG_INT on linux, and invoking the magic code that exists inside procinterrupt.cpp on windows.