[NFC] remove explicit default value for strboolattr attribute in tests

Since d6de1e1a71406c75a4ea4d5a2fe84289f07ea3a1, no attributes is quivalent to
setting attribute to false.

This is a preliminary commit for https://reviews.llvm.org/D99080

GitOrigin-RevId: bda6e5bee04c75b1f1332b4fd1ac4e8ef6c3c247
71 files changed