parser: cleanup code for fixing comma bug

examples/count.pork

@@ -1,4 +1,4 @@
-export let count = 5
+let count = 5
 
 export func main() {
   var x = 1

parser/src/main/kotlin/gay/pizza/pork/parser/Parser.kt

@@ -60,11 +60,7 @@ class Parser(source: PeekableSource<Token>, val attribution: NodeAttribution) {
   private fun readSymbolCases(): Expression = within {
     val symbol = readSymbolRaw()
     if (next(TokenType.LeftParentheses)) {
-      val arguments = collect(
+      val arguments = collect(TokenType.RightParentheses, TokenType.Comma) {
-        TokenType.RightParentheses,
-        TokenType.Comma,
-        forceConsumeExceptLast = true
-      ) {
         readExpression()
       }
       expect(TokenType.RightParentheses)
@@ -363,19 +359,16 @@ class Parser(source: PeekableSource<Token>, val attribution: NodeAttribution) {
   private fun <T> collect(
     peeking: TokenType,
     consuming: TokenType? = null,
-    forceConsumeExceptLast: Boolean = false,
     read: () -> T
   ): List<T> {
     val items = mutableListOf<T>()
     while (!peek(peeking)) {
       val item = read()
       if (consuming != null) {
-        if (!next(consuming)) {
         if (!peek(peeking)) {
           expect(consuming)
         }
       }
-      }
       items.add(item)
     }
     return items