Remove extraneous constructors from QgsCoordinateTransform?

[nyalldawson]

I'd like to remove some constructors from QgsCoordinateTransform, specifically:

• QgsCoordinateTransform( long theSourceSrsId, long theDestSrsId );
• QgsCoordinateTransform( const QString& theSourceWkt, const QString& theDestWkt );
• QgsCoordinateTransform( long theSourceSrid, const QString& theDestWkt, QgsCoordinateReferenceSystem::CrsType theSourceCRSType = QgsCoordinateReferenceSystem::PostgisCrsId );

Why? Well, I think all the use cases for constructing this way are much better addressed in QgsCoordinateReferenceSystem itself. I'd suggest we leave only the QgsCoordinateTransform( const QgsCoordinateReferenceSystem& theSource, const QgsCoordinateReferenceSystem& theDest ); constructor (and the default, uninitialized constructor), and just require all QgsCoordinateReferenceSystem objects to be created in advance. The last one listed above is especially awkward API.

[nyalldawson]

Implemented in https://github.com/qgis/QGIS/commit/4a3924ca3fb163148ec5928aa90c81a741f71d03