ProjectExplorer: Simplify use of AbstractProcessStep::init()

1. Systematically check for AbstractProcessStep::init() first in
   derived classes.
2. Use setupProcessParameters(processParameters()); by default in
   the base implementation.
3. Drop all re-implementations that are effectively the same.

Change-Id: I0ae54dd4909b354672a63ee56d0b7c2ea0732494
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/ios/iosdsymbuildstep.cpp

@@ -70,19 +70,11 @@ IosDsymBuildStep::IosDsymBuildStep(BuildStepList *parent, Id id) :
 {
     setCommandLineProvider([this] { return CommandLine(command(), arguments()); });
     setUseEnglishOutput();
-}
-
-bool IosDsymBuildStep::init()
-{
-    ProcessParameters *pp = processParameters();
-    setupProcessParameters(pp);
 
     // If we are cleaning, then build can fail with an error code, but that doesn't mean
     // we should stop the clean queue
     // That is mostly so that rebuild works on an already clean project
     setIgnoreReturnValue(m_clean);
-
-    return AbstractProcessStep::init();
 }
 
 QVariantMap IosDsymBuildStep::toMap() const