Do not use "--debug-brk" if a runtimeExecutable is specified

[weinand]

Currently node-debug2 passes a combination of "--inspect" and "--debug-brk" flags when launching node.js (and any other "runtimeExecutable"). This is done because node.js versions < v8.0 do not support "--inspect-brk" but instead the combination only).

Since I'm not sure that Electron (or other runtimeExecutables) will support this combination too, I suggest that we stop using the combination whenever a runtimeExecutable is specified.

Does this make sense?

See microsoft/vscode#30504 (comment)

[roblourens]

I just put microsoft/vscode#27731 on the July milestone, I'll track it there.