Fix incorrect math equation renderings in random_fourier_features.py (#18367)

* Fix incorrect math equation renderings in random_fourier_features.py

This fix fixes incorrect math equation renderings for markdown
in random_fourier_features.py. The issue is that
"```" backtick should not be added when mathjax quote is used ("\\(" or "$$").

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Additional fix.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* MathJax fixes

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Fix pylint errors

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>