[llvm-symbolizer] Remove one-dash long options

Most modern tools only accept two-dash long options. Remove one-dash
long options which are not recognized by GNU style `getopt_long`.
This ensures long options cannot collide with grouped short options.

Note: llvm-symbolizer has `-demangle={true,false}` for pprof compatibility
(for a while). They are kept.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D106377