Use PST hr styling

Author: jarrodmillman

assets/theme-css/bulma.css

@@ -162,12 +162,6 @@ header,
 section {
   display: block;
 }
-hr {
-  border: none;
-  display: block;
-  height: 2px;
-  margin: 1.5rem 0;
-}
 img {
   height: auto;
   max-width: 100%;

assets/theme-css/styles.css

@@ -6,10 +6,6 @@ body {
   color: var(--pst-heading-color);
 }
 
-hr {
-  background-color: var(--pst-color-text-muted);
-}
-
 /**
  * See `code.literal` in
  * src/pydata_sphinx_theme/assets/styles/content/_code.scss