Add unused-descriptors.wast to fuzzer ignore list (#7795)

Author: tlively

scripts/test/fuzzing.py

@@ -136,6 +136,7 @@
     'vacuum-desc.wast',
     'j2cl-merge-itables-desc.wast',
     'heap-store-optimization-desc.wast',
+    'unused-descriptors.wast',
     # TODO: fix split_wast() on tricky escaping situations like a string ending
     #       in \\" (the " is not escaped - there is an escaped \ before it)
     'string-lifting-section.wast',