Remove adjustments that used to be necessary for search's crate selector appearance (padding)

to look identical on Firefox. New versions of Firefox appear to have changed behavior to agree with Chrome.

src/librustdoc/html/static/css/rustdoc.css

@@ -776,7 +776,6 @@ table,
 }
 #crate-search {
 	min-width: 115px;
-	/* keep these two in sync with "@-moz-document url-prefix()" below */
 	padding: 0 23px 0 4px;
 	/* prevents the <select> from overflowing the containing div in case it's shrunk */
 	max-width: 100%;
@@ -798,14 +797,6 @@ table,
 #crate-search:hover, #crate-search:focus {
 	border-color: var(--crate-search-hover-border);
 }
-/* cancel stylistic differences in padding in firefox
-for "appearance: none"-style (or equivalent) <select>s */
-@-moz-document url-prefix() {
-	#crate-search {
-		padding-left: 0px; /* == 4px - 4px */
-		padding-right: 19px; /* == 23px - 4px */
-	}
-}
 /* pseudo-element for holding the dropdown-arrow image; needs to be a separate thing
 so that we can apply CSS-filters to change the arrow color in themes */
 #crate-search-div::after {