[dartfuzz] Fix trybot breakage

`DartType.VOID` and `DartType.VOID_NULLABLE` are the same constant,
therefore only one of them should be listed in
`DartLib.typeToLibraryMethods`, to avoid an `equal_keys_in_map`
warning.

Change-Id: I65beef01f8a810af96be5e458eeecef7a7acff01
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/321820
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>
Auto-Submit: Paul Berry <paulberry@google.com>

runtime/tools/dartfuzz/dartfuzz_api_table.dart

diff --git a/runtime/tools/dartfuzz/dartfuzz_api_table.dart b/runtime/tools/dartfuzz/dartfuzz_api_table.dart
index 8f08f4e..4b59975 100644
--- a/runtime/tools/dartfuzz/dartfuzz_api_table.dart
+++ b/runtime/tools/dartfuzz/dartfuzz_api_table.dart
@@ -86,7 +86,6 @@
     DartType.UINT8CLAMPEDLIST_NULLABLE: uint8ClampedListLibsNullable,
     DartType.UINT8LIST: uint8ListLibs,
     DartType.UINT8LIST_NULLABLE: uint8ListLibsNullable,
-    DartType.VOID: voidLibs,
     DartType.VOID_NULLABLE: voidLibsNullable,
   };
   static const typedDataFloatTypes = [