Revert "Include shim-signed"

This is temporary to allow component re-use of the old build for testing
signed composes.  I will be putting this back, along with a new gc "fix"
and changing the bootstrap BR to the f26 stream.

This reverts commit b613857b5e.

base-runtime.yaml

@@ -13,7 +13,6 @@ data:
     dependencies:
         buildrequires:
             bootstrap: master
-            shim: master
     references:
         community: https://fedoraproject.org/wiki/BaseRuntime
         documentation: https://github.com/fedora-modularity/base-runtime
@@ -517,8 +516,6 @@ data:
             sgml-common, xml-common,
             # shadow-utils
             shadow-utils,
-            # shim-signed
-            shim,
             # sqlite
             lemon, sqlite, sqlite-devel, sqlite-doc, sqlite-libs,
             # syslinux
@@ -1341,10 +1338,6 @@ data:
             shadow-utils:
                 rationale: Autogenerated by Base Runtime tools.
                 ref: ba9340caf5a3f86043659dd5dc83d9280cd38185
-            # shim-signed-0.8-10.1.*
-            shim-signed:
-                rationale: Autogenerated by Base Runtime tools.
-                ref: bb890e80b23392d1ac40c5dbb3770acfa1ef5d6c
             # sqlite-3.17.0-2.fc26
             sqlite:
                 rationale: Autogenerated by Base Runtime tools.