chore: Remove unused exception ConnectionException

[tienvx]

The exception ConnectionException is for version <=9 when user work with mock server directly.
At version 10, mock server is automatically started and stopped, so this exception is no longer needed

[Lewiscowles1986]

Approved, but logically, this speaks to a degredation in code quality as we can't discern specific classes of errors.

[tienvx]

At version 10, mock server is automatically started and stopped, so this exception is no longer needed

I was wrong about this. I mean:

At version 10, user doesn't work with mock server directly, so this exception is no longer needed