Update comments in toolchain to point to new names of files (#3264)

toolchain/lex/tokenized_buffer_fuzzer.cpp

@@ -19,7 +19,7 @@ extern "C" int LLVMFuzzerTestOneInput(const unsigned char* data,
   // escaped quotes (`\"` repeated) have O(M * N) behavior for M errors in a
   // file length N, so either that will need to also be fixed or M will need to
   // shrink for large (1MB+) inputs.
-  // This also affects parse_tree_fuzzer.cpp.
+  // This also affects parse/parse_fuzzer.cpp.
   if (size > 100000) {
     return 0;
   }