Remove topics frontmatter from content/migrations (#59971)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: subatoi <32935794+subatoi@users.noreply.github.com>

Author: Copilot

content/migrations/importing-source-code/index.md

@@ -5,7 +5,6 @@ versions:
   fpt: '*'
   ghec: '*'
   ghes: '*'
-# topics:
 redirect_from:
   - /categories/67/articles
   - /categories/importing

content/migrations/importing-source-code/using-the-command-line-to-import-source-code/index.md

@@ -5,7 +5,6 @@ versions:
   fpt: '*'
   ghec: '*'
   ghes: '*'
-# topics:
 children:
   - /about-source-code-imports-using-the-command-line
   - /adding-locally-hosted-code-to-github