[fuzzer] Relax the FileCheck string for test fuzzer-custommutator.test (

#66343)

The FileCheck string `LLVMFuzzerCustomMutatorLongSequence: {{.*}} MS:
{{[0-9]*}} {{(([a-zA-Z]*-){11,})}} {{.*}}` is too restrictive and may
fail the test in some case.

If we look at the commit that added this
check(66df989),
This check is for printing out the long mutation sequence, such as this
one
```
#53552  REDUCE cov: 6 ft: 6 corp: 5/9b lim: 4096 exec/s: 0 rss: 37Mb L: 2/3 MS: 54 ChangeByte-PersAutoDict-ChangeBit-ChangeBinInt-ChangeBit-ChangeBit-ChangeByte-CMP-EraseBytes-EraseBytes-CrossOver-InsertRepeatedBytes-ChangeByte-EraseBytes-InsertRepeatedBytes-ShuffleBytes-ChangeByte-ShuffleBytes-ChangeBit-CrossOver-ChangeBit-ShuffleBytes-ChangeBinInt-ShuffleBytes-EraseBytes-InsertByte-Custom-ShuffleBytes-CopyPart-InsertRepeatedBytes-PersAutoDict-InsertRepeatedBytes-ChangeByte-CrossOver-CrossOver-PersAutoDict-PersAutoDict-EraseBytes-ChangeBit-CopyPart-ChangeByte-CopyPart-InsertRepeatedBytes-CrossOver-CrossOver-CrossOver-CrossOver-ShuffleBytes-EraseBytes-InsertByte-InsertRepeatedBytes-CrossOver-EraseBytes-Custom- DE: "\377\377"-"\001\000"-"\001\000"-"\000\000\000\000\000\000\000\000"-"\001\000\000\000"-
```

But if we look at the code doing the printing
```cpp
void MutationDispatcher::PrintMutationSequence(bool Verbose) {
  Printf("MS: %zd ", CurrentMutatorSequence.size());
  size_t EntriesToPrint =
      Verbose ? CurrentMutatorSequence.size()
              : std::min(kMaxMutationsToPrint, CurrentMutatorSequence.size());
  for (size_t i = 0; i < EntriesToPrint; i++)
    Printf("%s-", CurrentMutatorSequence[i].Name);
  if (!CurrentDictionaryEntrySequence.empty()) {
    Printf(" DE: ");
    EntriesToPrint = Verbose ? CurrentDictionaryEntrySequence.size()
                             : std::min(kMaxMutationsToPrint,
                                        CurrentDictionaryEntrySequence.size());
    for (size_t i = 0; i < EntriesToPrint; i++) {
      Printf("\"");
      PrintASCII(CurrentDictionaryEntrySequence[i]->GetW(), "\"-");
    }
  }
}
```

We can see that the `DE: XXX` is not always printed. So the following
output is possible(and is from real-life failure), notince the missing
of `DE: XXX`.
```
#13613  NEW    cov: 5 ft: 5 corp: 4/6b lim: 4096 exec/s: 0 rss: 32Mb L: 2/2 MS: 27 InsertByte-ChangeBinInt-ChangeBinInt-CrossOver-ShuffleBytes-ChangeBit-EraseBytes-ShuffleBytes-InsertByte-InsertRepeatedBytes-CopyPart-InsertByte-ChangeByte-ChangeBit-InsertByte-CrossOver-EraseBytes-CopyPart-ShuffleBytes-EraseBytes-InsertByte-InsertRepeatedBytes-CrossOver-CrossOver-ShuffleBytes-ChangeBit-Custom-
#13765  ......
```
This output is totally legit and will fail that check.

So I remove the check for the following strings, I think `MS: {{[0-9]*}}
{{(([a-zA-Z]*-){11,})}}` is sufficient for checking the long mutation
sequence. This should help resolve the flaky failure of
fuzzer-custommutator.test.

compiler-rt/test/fuzzer/fuzzer-custommutator.test

@@ -16,7 +16,7 @@ LLVMFuzzerCustomMutatorWithLenControl: BINGO
 RUN: %cpp_compiler %S/CustomMutatorWithLongSequencesTest.cpp -o %t-CustomMutatorWithLongSequencesTest
 RUN: not %run %t-CustomMutatorWithLongSequencesTest -verbosity=2 2>&1 | FileCheck %s --check-prefix=LLVMFuzzerCustomMutatorLongSequence
 LLVMFuzzerCustomMutatorLongSequence: Flag: verbosity 2
-LLVMFuzzerCustomMutatorLongSequence: {{.*}} MS: {{[0-9]*}} {{(([a-zA-Z]*-){11,})}} {{.*}}
+LLVMFuzzerCustomMutatorLongSequence: {{.*}} MS: {{[0-9]*}} {{(([a-zA-Z]*-){11,})}}
 LLVMFuzzerCustomMutatorLongSequence: BINGO
 
 # check a target that prints long mutation sequences and verifies the printed