Deprecate unused QgsProcessingAlgorithm::helpString method

Author: nyalldawson

python/core/auto_generated/processing/qgsprocessingalgorithm.sip.in

@@ -140,14 +140,16 @@ about what the algorithm does and the parameters and outputs associated with it.
 .. seealso:: :py:func:`helpUrl`
 %End
 
-    virtual QString helpString() const;
+ virtual QString helpString() const /Deprecated/;
 %Docstring
 Returns a localised help string for the algorithm. Algorithm subclasses should implement either
 helpString() or helpUrl().
 
 .. seealso:: :py:func:`helpUrl`
 
 .. seealso:: :py:func:`shortHelpString`
+
+.. deprecated:: Unused, will be removed in QGIS 4.0
 %End
 
     virtual QString helpUrl() const;

src/core/processing/qgsprocessingalgorithm.h

@@ -183,8 +183,9 @@ class CORE_EXPORT QgsProcessingAlgorithm
      * helpString() or helpUrl().
      * \see helpUrl()
      * \see shortHelpString()
+     * \deprecated Unused, will be removed in QGIS 4.0
      */
-    virtual QString helpString() const;
+    Q_DECL_DEPRECATED virtual QString helpString() const SIP_DEPRECATED;
 
     /**
      * Returns a url pointing to the algorithm's help page.