Remove unused pats and field-pats grammars (#88)

Author: roboz0r

spec/patterns.md

@@ -66,8 +66,6 @@ pat-param :=
     '<@@' expr '@@>'
     null
 
-pats := pat ',' ... ',' pat
-field-pats := field-pat ';' ... ';' field-pat
 rules := '|'? rule '|' ... '|' rule
 ```