.pytool: Remove SignedCapsulePkg

Remove SignedCapsulePkg from the following .pytool files:

- CISettings.py: Remove SignedCapsulePkg from the GetPackagesSupported()
  list to exclude it from CI build and test operations.
- Readme.md: Remove the SignedCapsulePkg row from the package status
  table.

SignedCapsulePkg is no longer used. The features provided by this
package have been superseded by FmpDevicePkg.

Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>