[DOC] Remove ..figure directive in examples

[skoudoro]

Sphinx gallery generate its own figure directive. So, currently our ..figure directive are not processed and shows unfound files in our tutorials which is confusing.

Furthermore, I added .. rst-class:: centered small fst-italic fw-semibold directive to simulate and not lose some captions.

[codecov]

Codecov Report

Merging #2944 (b1d2d74) into master (3ad9ec1) will decrease coverage by 0.06%.
Report is 157 commits behind head on master.
The diff coverage is 80.00%.

❗ Current head b1d2d74 differs from pull request most recent head fbc1d04. Consider uploading reports for the commit fbc1d04 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2944      +/-   ##
==========================================
- Coverage   81.77%   81.71%   -0.06%     
==========================================
  Files         146      147       +1     
  Lines       20401    20484      +83     
  Branches     3238     3277      +39     
==========================================
+ Hits        16682    16739      +57     
- Misses       2901     2913      +12     
- Partials      818      832      +14     

Files	Coverage Δ
dipy/data/fetcher.py	40.25% <ø> (ø)
dipy/info.py	100.00% <100.00%> (ø)
dipy/io/stateful_tractogram.py	76.96% <100.00%> (ø)
dipy/reconst/dti.py	92.57% <0.00%> (ø)
dipy/tracking/local_tracking.py	94.44% <96.29%> (ø)
dipy/io/utils.py	88.83% <90.00%> (ø)
dipy/io/streamline.py	84.92% <75.00%> (ø)
dipy/align/imwarp.py	95.60% <37.50%> (ø)

... and 13 files with indirect coverage changes

[skoudoro]

Ok, this PR is ready to go.

is there any comments/suggestions ? I will go ahead and merge this tomorrow at noon if no comments.

This cleaning was needed and more to come after the release.

[arokem]

Looks good to me! I spotted a couple of typos along the way, but that doesn't mean there aren't any other ones :-)

[skoudoro]

thank you for the review @arokem!

For sure there is other ones, like old functions a simpler way to do stuff in many tutorials. We will continue to update that.during the year.

[skoudoro]

ps: building the doc in parallel, just waiting the build to finish before merging this PR.

[skoudoro]

ok, all good, merging