[lldb/Commands] Fix outdated `breakpoint command add` help string

Update the some examples in the help string for `breakpoint command add`.

Python breakpoint commands have different output than what's shown in the help string.

Notes:
  * Removed an example containing an inner function, as it seems more about a Python technique than about `command script add`
  * Updated `print x` to `print(x)` to be python 2/3 agnostic

Differential Revision: https://reviews.llvm.org/D87807