Simplify the libcxx std::string_view gdb pretty printer

Seems better to rely on the existing formatting, makes the output
smaller/simpler - this is consistent with libstdc++'s std::string_view
pretty printing too.

Differential Revision: https://reviews.llvm.org/D113244

NOKEYCHECK=True
GitOrigin-RevId: ff618a963aa52b9d2206f4ec83920b0e76535288
2 files changed