py3: finish porting iteritems() to pycompat and remove source transformer This commit finishes porting .iteritems() to pycompat.iteritems() for the mercurial package. The translation of .iteritems() to .items() was the last conversion performed by the source transformer. With the porting to pycompat complete, we no longer have a need for the source transformer. So the source transformer has been removed. Good riddance! The code base is now compatible with Python 2 and Python 3. For the record, as the person who introduced the source transformer, it brings me joy to delete it. It accomplished its goal to facilitate a port to Python 3 without overly burdening people on some painful low-level differences between Python 2 and 3. It is unfortunate we still have to wallpaper over many differences with the pycompat shim. But it is what it is. Differential Revision: https://phab.mercurial-scm.org/D7015

py3: define and use pycompat.iteritems() for hgext/ .iteritems() -> .items() is the last source transform being performed. But it is also the most widely used. This commit adds a pycompat.iteritems symbol and imports it in place of .iteritems() for usage in hgext/. I chose to stop at just hgext/ because the patch will be large and it is an easy boundary to stop at since we can disable source transformation on a per-package basis. There are places where the type does implement items() and we could call items() directly. However, this would require critical thought and I thought it would be easier to just blindly change the code. We know which call sites need to be audited in the future because they have "pycompat.iteritems." With this change, we no longer perform source transformation on hgext! Differential Revision: https://phab.mercurial-scm.org/D7014