remove check for contributing page from validate_site.py

Author: ncclementi

scripts/validate_site.py

@@ -22,7 +22,6 @@
     "SECURITY.md",
     "404.html",
     "api/index.html",
-    "contributing/index.html",
     "install/index.html",
     "maintainers/index.html",
     "notices/index.html",