lib: remove unused internal error constructors

First commit removes exports for internal error constructors. Now all internal errors must be thrown using the new system: throw new errors.codes.MY_ERROR('xxx') instead of throw new errors.Error('MY_ERROR', 'xxx').

Second commit updates the internal errors documentation following this change.

@BridgeAR I tried to move SystemError to makeNodeErrorWithCode but it's not obvious to me how that could be done because the error code is not fixed, so I left it as is for now.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines