[lldb][NFCI] Remove unneeded ConstString constructions for OptionValueProperties::AppendProperty

I removed ConstString from OptionValueProperties in 643ba926, but
there are a few call sites that still create a ConstString as an
argument. I did not catch these initially because ConstString has an
implicit conversion method to StringRef.

Differential Revision: https://reviews.llvm.org/D153673