Remove unwanted R code

[SarithaKodikara]

In the episode exploring data frames (https://swcarpentry.github.io/r-novice-gapminder/05-data-structures-part2.html), renaming row names is unnecessary as R re-names them sequentially. So, in the section 'Append to a data frame', the following code snippet can be removed.

If this pull request addresses an open issue on the repository, please add 'Closes #NN' below, where NN is the issue number.
Closes #873

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Rendered Changes

🔍 Inspect the changes: https://github.com/swcarpentry/r-novice-gapminder/compare/md-outputs..md-outputs-PR-877

The following changes were observed in the rendered markdown documents:

 05-data-structures-part2.md | 23 +----------------------
 md5sum.txt                  |  2 +-
 2 files changed, 2 insertions(+), 23 deletions(-)

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If you have source files that require output and figures to be generated (e.g. R Markdown), then it is important to make sure the generated figures and output are reproducible.

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⏱️ Updated at 2023-11-21 14:41:36 +0000

[matthieu-bruneaux]

Thank you very much for your contribution @SarithaKodikara! This is very helpful to keep the lesson material up to date.

I took the liberty to remove the mention of rownames() in the lesson key points to have them consistent with your changes.