DEVDOCS-6077: [update] remove style guide references (#566)

<!-- Ticket number or summary of work -->
# [DEVDOCS-6077]


## What changed?
These links go to placeholders. There is no information, therefore,
removing them.

## Release notes draft
N/A

## Anything else?
<!-- Add related PRs, salient notes, additional ticket numbers, etc. -->

ping {names}


[DEVDOCS-6077]:
https://bigcommercecloud.atlassian.net/browse/DEVDOCS-6077?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

CONTRIBUTING.md

@@ -54,11 +54,6 @@ For more complex changes, fork and edit locally:
 - Do not end the subject line with a period.
 - Use the body to explain what and why versus how.
 
-## Style Guides
-
-- [Documentation Style Guide](_project/_doc_style_guide.md)
-- [API Specification Style Guide](_project/_spec_style_guide.md)
-
 ## Contributing to Other Projects
 
 There are many other public BigCommerce repositories accepting contributions. If you're interested in contributing to those projects, see the [full list of public source repos](https://github.com/bigcommerce?utf8=%E2%9C%93&q=is%3Apublic&type=source&language=). Also, consider joining the [BigCommerce Developer Community](https://developer.bigcommerce.com/community).