Use pydevd frame id's instead of generating frame ids

[karthiknadig]

Currently we generate frame ids that we send back to the IDE. We keep a map in the debugger. This causes issues when stepping in the IDE, where at each step the variables window will collapse expanded variables.

[karthiknadig]

See #910 for the fix that preserves frame ids. Using pydevd frame ids will allows us to remove some of the bookkeeping that we do. This is not necessary to fix the collapsed variables issue.

[karthiknadig]

This is not needed since we will be using DAP directly with pydevd