STYLE: Remove empty comment lines in itk::TriangleCell implementation

[jhlegarreta]

Remove unnecessary single-comment, empty lines when introducing comment blocks in itk::TriangleCell implementation.

PR Checklist

• No API changes were made (or the changes have been approved)
• No major design changes were made (or the changes have been approved)

[jhlegarreta]

This behavior is allowed by the ITK SW Guide:
https://github.com/InsightSoftwareConsortium/ITKSoftwareGuide/blob/master/SoftwareGuide/Latex/Appendices/CodingStyleGuide.tex#L2909

The commit started when I changed the whitespaces between the comment character and the comment itself in
https://github.com/InsightSoftwareConsortium/ITK/pull/4114/files#diff-0f33d6ca3071b761eafeb4067fd7a2404113a7722283834a7869701bddeb2d29L305
and when finding other single-line, empty lonely comments:
https://github.com/InsightSoftwareConsortium/ITK/pull/4114/files#diff-0f33d6ca3071b761eafeb4067fd7a2404113a7722283834a7869701bddeb2d29L540

If the behavior should be discouraged, happy to make a PR to the ITK SW Guide; if we think it makes the code more readable, then happy to modify this commit to only remove the whitespaces in
https://github.com/InsightSoftwareConsortium/ITK/pull/4114/files#diff-0f33d6ca3071b761eafeb4067fd7a2404113a7722283834a7869701bddeb2d29L305

[dzenanz]

I wholeheartedly agree with this change. Maybe this style of comments has the "advantage" of raising number of comment lines with little effort. I find it highly annoying, as it wastes vertical real estate.

[dzenanz]

Adding a PR to software guide would be good too!

[jhlegarreta]

Adding a PR to software guide would be good too!

InsightSoftwareConsortium/ITKSoftwareGuide#203