Use dict instead of OrderedDict

[yarikoptic]

dict is ordered now in versions of python we support. And according to https://realpython.com/python-ordereddict/ - dict seems to generally outperform OrderedDict in CPU and memory, and I don't think we use any of specific to OrderedDict functionality.

(git)lena:~datalad/datalad-maint[bf-sve]git
$> git grep OrderedDict | wc -l 
64

I think it would not hurt to just switch to just use dict.

[adswa]

I believe I found one specific use of OrderedDict, namely popitem(last=False), used in status:

datalad/core/local/status.py:635:        qdspath, qpaths = paths_by_ds.popitem(last=False)

The standard dict's popitem method doesn't take arguments, and returns items in LIFO order, but the last=False parameter in OrderedDicts results in FIFO order.

[yarikoptic]

good catch! popitem(last=False) could be replaced with some helper like

k = next(iter(d.keys())); v = d.pop(k)

I guess. The key would be the first one. If a singular use, could be just applied as above without carrying to create a helper.

[adswa]

done in #7174

[yarikoptic-gitmate]

Issue fixed in 0.18.0