Fuzz input fix for function type literal changed in #1272 (#1289)

This reverts commit aa7c98802cb7caa6b8954572dbc8b3e56a0a1181.

explorer/fuzzing/fuzzer_corpus/512e48e65ff569c91b7cbebbb6160b07de5b2ab1.textproto → explorer/fuzzing/fuzzer_corpus/00f0094e829126778228c3fdefec8654ceab30e4.textproto

@@ -7,7 +7,9 @@ compilation_unit {
             expression {
               function_type {
                 parameter {
-                  primitive_operator {
+                  fields {
+                    primitive_operator {
+                    }
                   }
                 }
               }