docs: drop obselete theme fixes

docs/_static/css/custom.css

@@ -8,38 +8,3 @@
 .rst-content div[class^='highlight'] pre {
 	overflow: visible;
 }
-
-
-/*
-  This fixes the bottom margin of paragraphs inside lists, where margins inside
-  a single list item would incorrectly be displayed larger than margins between
-  the list items.
-
-  Upstream fix (not fixed on readthedocs.io yet):
-  https://github.com/readthedocs/sphinx_rtd_theme/commit/ac20ce75d426efeb40fe2af1f89ea9bad285a45b
-*/
-.rst-content .section ol li > p,
-.rst-content .section ol li > p:last-child,
-.rst-content .section ul li > p,
-.rst-content .section ul li > p:last-child {
-	margin-bottom: 12px;
-}
-.rst-content .section ol li > p:only-child,
-.rst-content .section ol li > p:only-child:last-child,
-.rst-content .section ul li > p:only-child,
-.rst-content .section ul li > p:only-child:last-child {
-	margin-bottom: 0rem;
-}
-
-/*
-  This fixes the bottom margin of nested lists
-
-  Based on upstream fix (not on readthedocs.io yet):
-  https://github.com/readthedocs/sphinx_rtd_theme/commit/6f0de13baff93f25204aa2cdf0308aae47d71312
-*/
-.rst-content .section ul li > ul,
-.rst-content .section ul li > ol,
-.rst-content .section ol li > ul,
-.rst-content .section ol li > ol {
-	margin-bottom: 12px;
-}