BOUT++ fails with most recent version

[dschwoerer]

Traceback (most recent call last):
  File "/home/test/BOUT-dev/build/tests/integrated/test-drift-instability/runtest", line 10, in <module>
    from boututils.file_import import file_import
ModuleNotFoundError: No module named 'boututils.file_import'

Was that deleted in https://github.com/boutproject/boutdata/pull/112/files#diff-377222da5cb71dc6fafc0e1bf783eb448fa3418169de03b3013c151982ba0c4c

[dschwoerer]

There are 60 uses in 41 files:

[dave@panhu: BOUT-dev]👍 git grep file_import|wc
     60     189    4486
[dave@panhu: BOUT-dev]👍 git grep file_import|cut -d: -f1| uniq|wc
     41      41    1516

Some are .pro files, but several are py.
They are also used in the examples, so likely also in production code.

Assuming this is not inherently broken (which does not seem to be the case) I will revert this ...

[ZedThree]

Thanks, nice catch @dschwoerer

DataFile now has __getitem__, so I think this can still be removed, but probably best fix uses of it first