Drop fatal error else case when trying to update submodules

[hellkite500]

The error condition this was originally trapping doesn't seem relevant, and results in a fatal build error when the submodule build option is disabled, even thought it shouldn't be.

Changes

• don't error build if ngen submodules are not requested

Checklist

• [x] PR has an informative and human-readable title
• [x] Changes are limited to a single goal (no scope creep)
• [x] Code can be automatically merged (no conflicts)
• [x] Code follows project standards (link if applicable)
• [x] Passes all existing automated tests
• [x] Any change in functionality is tested
• [x] New functions are documented (with a description, list of inputs, and expected output)
• [x] Placeholder code is flagged / future todos are captured in comments
• [x] Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• [x] Reviewers requested with the Reviewers tool :arrow_right:

Testing checklist

1. Build tested locally

Target Environment support

• [x] Linux
• [x] MacOS

[PhilMiller]

The change looks good to me, but I'm a bit confused about the code that's being removed. The error message seems incongruous with the logic