remove unnecessary 'relativepath' warning/error case for html links

Linking

...

we were 'warn/erroring' on path links that were valid but relative, even if the file was able to load properly

allow for relative links

nope

before, we're getting a lot of unnecessary warnings:

now we're no longer getting those warnings:

[x] PASS - all necessary actions must pass (excluding the auto-skipped ones)
[x] TEST IN HEADSET - main dev-testing-example and any of the other examples still work as expected
~~[ ] VIDEO - if this pr changes something visually - post a video here of it in headset-MR and/or on desktop (depending on what it affects) for the reviewer to reference.~~
[x] TITLE - make sure the pr's title is updated appropriately as it will be used to name the commit on merge
[ ] BREAKING CHANGE
- DOCUMENTATION: This includes any changes to html tags and their components
- make a pr in the documentation repo that updates the manual docs to match the breaking change
- link the pr of the documentation repo here: #pr
- that pr must be approved by @lobau
- SAMPLES/INDEX.HTML: This includes any changes (html tags or otherwise) that must be done to our landing page submodule as an effect of this pr's updates
- make a pr in the mrjs landing page repo that updates the landing page to match the breaking change
- link the pr of the landing page repo here: #pr
- that pr must be approved by @hanbollar