unified: drop element field on _parenthesized_type

Same pattern we've seen many times before: a field on an anonymous node
gets attached to the parent node instead.

I'm not 100% sure this is the right solution, but it seemed wrong to
just make `_parenthesized_type` named instead (we don't usually name
parentheticals). At the very least, this cleans up the spurious
navigation_expression.element and tuple_type_item.element fields.

Author: tausbn

unified/extractor/tree-sitter-swift/grammar.js

@@ -567,10 +567,7 @@ module.exports = grammar({
     _parenthesized_type: ($) =>
       seq(
         "(",
-        field(
-          "element",
-          choice($.opaque_type, $.existential_type, $.dictionary_type)
-        ),
+        choice($.opaque_type, $.existential_type, $.dictionary_type),
         ")"
       ),
     navigation_expression: ($) =>