Correct the argument list of command `breakpoint read`

Summary: Command `breakpoint read` should not accept breakpoint ids as
arguments, and in fact, it is not implemented to deal with breakpoint id
arguments either. So this patch is to correct the argument list of this
command so that the help text won't misguide users.

Reviewers: teemperor, JDevlieghere, jingham

Reviewed By: teemperor, JDevlieghere

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D79722