Remove unused method

Author: bioball

pkl-parser/src/main/java/org/pkl/parser/GenericParser.java

@@ -48,11 +48,6 @@ private void init(String source) {
     spanLookahead = _lookahead.span;
   }
 
-  public Node parseExpression(String source) {
-    init(source);
-    return parseExpr();
-  }
-
   public Node parseModule(String source) {
     init(source);
     if (lookahead == Token.EOF) {