FIX: Restore AFNICommand._get_fname, required by some interfaces

[oesteban]

In #2964 I broke some interfaces (@tsalo identified Allineate as one
of those) by removing the _get_fname function from the base
AFNICommand.

The intent was to migrate to a name_source-based management of
automatically generated names, but in the case of Allineate, the use
of _get_fname was a bit different (modifying the user-provide input
value under certain conditions to follow ANFI's 3dAllineate
behavior).

This PR restores the missing function. Closes #3070.

Summary

Fixes # .

List of changes proposed in this PR (pull-request)

Acknowledgment

• (Mandatory) I acknowledge that this contribution will be available under the Apache 2 license.

[effigies]

Should we re-add to just Allineate? I suggest this from my phone, without looking closely at it.

[codecov]

Codecov Report

Merging #3071 into master will decrease coverage by 3.52%.
The diff coverage is 37.5%.

@@            Coverage Diff             @@
##           master    #3071      +/-   ##
==========================================
- Coverage    67.7%   64.17%   -3.53%     
==========================================
  Files         344      342       -2     
  Lines       44111    44027      -84     
  Branches     5563     5552      -11     
==========================================
- Hits        29866    28255    -1611     
- Misses      13480    14653    +1173     
- Partials      765     1119     +354

Flag	Coverage Δ
#smoketests	?
#unittests	64.17% <37.5%> (-0.96%)	⬇️

Impacted Files	Coverage Δ
nipype/interfaces/afni/model.py	87% <ø> (+4.95%)	⬆️
nipype/interfaces/afni/base.py	67.76% <37.5%> (-4.88%)	⬇️
nipype/interfaces/nilearn.py	40% <0%> (-56.67%)	⬇️
nipype/utils/spm_docs.py	25.92% <0%> (-44.45%)	⬇️
nipype/interfaces/freesurfer/base.py	50% <0%> (-30.51%)	⬇️
nipype/utils/logger.py	59.7% <0%> (-29.86%)	⬇️
nipype/algorithms/rapidart.py	35% <0%> (-29.42%)	⬇️
nipype/interfaces/spm/base.py	57.94% <0%> (-29.14%)	⬇️
nipype/utils/provenance.py	55.73% <0%> (-28.35%)	⬇️
nipype/interfaces/fsl/model.py	55.26% <0%> (-25.35%)	⬇️
... and 43 more

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[oesteban]

Unfortunately, a few more interfaces also got orphaned. I don't think it would be hard to migrate them to name_sources (esp. those under afni.utils), but I guess that's material for a different PR.

I also found that Deconvolve was defining the function, so removed it.

[effigies]

Sounds good.