LaTeX: avoid "The remreset package is obsolete" warnings in latex log

[jfbu]

With 2018 LaTeX, macro \@removefromreset is provided by kernel and loading remreset package creates this console output warning:

(/usr/local/texlive/2018/texmf-dist/tex/latex/carlisle/remreset.sty

Package remreset Warning: The remreset package is obsolete:
(remreset)                \@removefomresset is defined.

) (./sphinxhighlight.sty)

Avoid this warning by loading remreset only with older LaTeX.

[codecov]

Codecov Report

Merging #5237 into 1.7 will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              1.7    #5237      +/-   ##
==========================================
+ Coverage   82.02%   82.03%   +<.01%     
==========================================
  Files         283      288       +5     
  Lines       37879    38198     +319     
  Branches     5874     5928      +54     
==========================================
+ Hits        31071    31334     +263     
- Misses       5495     5542      +47     
- Partials     1313     1322       +9

Impacted Files	Coverage Δ
sphinx/apidoc.py	0% <0%> (ø)
sphinx/quickstart.py	0% <0%> (ø)
sphinx/__init__.py	57.5% <0%> (ø)
sphinx/errors.py	68.42% <0%> (ø)
sphinx/search/__init__.py	95.11% <0%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e955bcc...f5e38f4. Read the comment docs.