Remove table border-color special case (doesn't match reality)

Tests: will be upstreamed as part of https://bugzilla.mozilla.org/show_bug.cgi?id=1530048.

Fixes whatwg#4391.

source

@@ -112682,7 +112682,6 @@ caption { text-align: center; }
 thead, tbody, tfoot, table > tr { vertical-align: middle; }
 tr, td, th { vertical-align: inherit; }
 
-table, td, th { border-color: gray; }
 thead, tbody, tfoot, tr { border-color: inherit; }
 table[rules=none i], table[rules=groups i], table[rules=rows i],
 table[rules=cols i], table[rules=all i], table[frame=void i],
@@ -122390,6 +122389,7 @@ INSERT INTERFACES HERE
   Daniel Cheng,
   Daniel Davis,
   Daniel Glazman,
+  Daniel Holbert,
   Daniel Peng,
   Daniel Schattenkirchner,
   Daniel Spång,