PEP 538: Fix footnotes

[hugovk]

Fix these warnings:

pep-0538.txt:1181: WARNING: Footnote [1] is not referenced.
pep-0538.txt:1184: WARNING: Footnote [2] is not referenced.
pep-0538.txt:1187: WARNING: Footnote [3] is not referenced.
pep-0538.txt:1190: WARNING: Footnote [4] is not referenced.
pep-0538.txt:1193: WARNING: Footnote [5] is not referenced.
pep-0538.txt:1196: WARNING: Footnote [6] is not referenced.
pep-0538.txt:1199: WARNING: Footnote [7] is not referenced.
pep-0538.txt:1202: WARNING: Footnote [8] is not referenced.
pep-0538.txt:1205: WARNING: Footnote [9] is not referenced.
pep-0538.txt:1208: WARNING: Footnote [10] is not referenced.
pep-0538.txt:1211: WARNING: Footnote [11] is not referenced.
pep-0538.txt:1214: WARNING: Footnote [12] is not referenced.
pep-0538.txt:1217: WARNING: Footnote [13] is not referenced.
pep-0538.txt:1220: WARNING: Footnote [14] is not referenced.
pep-0538.txt:1223: WARNING: Footnote [15] is not referenced.
pep-0538.txt:1226: WARNING: Footnote [16] is not referenced.
pep-0538.txt:1229: WARNING: Footnote [17] is not referenced.
pep-0538.txt:1232: WARNING: Footnote [18] is not referenced.
pep-0538.txt:1235: WARNING: Footnote [19] is not referenced.
pep-0538.txt:1238: WARNING: Footnote [20] is not referenced.
pep-0538.txt:1241: WARNING: Footnote [21] is not referenced.
pep-0538.txt:1244: WARNING: Footnote [22] is not referenced.

The footnotes in the text should be of the form [1]_ not [1_].

• https://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html#footnotes

Also update some of the links to HTTPS and their redirects, and remove the redundant emacs metadata.

Preview

https://pep-previews--2714.org.readthedocs.build/pep-0538/