Revert "Add support for negative requirements"

This reverts commit b2068e80a814e5cf5c5d3786ea15747483bb236f.

This change does not appear to do the correct thing with "any" and
caused issues for us in production.  Our gate requirement of
jenkins>=+1 _and_ workflow=+1 became jenkins >=+1 or workflow=+1.

Change-Id: Ie5aa776b2dd718fcf025148073a0171332f358fb
diff --git a/tests/fixtures/layout-requirement-username.yaml b/tests/fixtures/layout-requirement-username.yaml
index 8520179..7a549f0 100644
--- a/tests/fixtures/layout-requirement-username.yaml
+++ b/tests/fixtures/layout-requirement-username.yaml
@@ -2,7 +2,7 @@
   - name: pipeline
     manager: IndependentPipelineManager
     require:
-      any-approval:
+      approval:
         - username: jenkins
     trigger:
       gerrit:
@@ -19,7 +19,7 @@
     trigger:
       gerrit:
         - event: comment-added
-          require-any-approval:
+          require-approval:
             - username: jenkins
     success:
       gerrit: