Documentation: virt/kvm: remove unreferenced footnote

Replace it with just the URL.

Reported-by: Stephen Rothwell <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: bonzini

Documentation/virt/kvm/x86/intel-tdx.rst

@@ -252,4 +252,4 @@ control flow is as follows:
 References
 ==========
 
-.. [1] https://www.intel.com/content/www/us/en/developer/tools/trust-domain-extensions/documentation.html
+https://www.intel.com/content/www/us/en/developer/tools/trust-domain-extensions/documentation.html