Part 3: Abstract pipeline_variables_form to its own component - clean up

What does this MR do and why?

Part 3 for #520831 (closed)

We are abstracting the pipeline variables form to it's own component in order to accommodate inputs work and also hide the component depending on settings.

Part 3 removes the redundant pipeline variables code

Step	MR
Set up component/query	!182376 (merged)
Build out pipeline variable form component	!182455 (merged)
Clean up and integration	[Current MR]

Screenshots or screen recordings

No UI change

How to set up and validate locally

1. Navigate to Build > Pipeline editor and enter the following into your gitlab-ci.yml

variables:
  DEPLOY_ENVIRONMENT:
    value: "staging"
    options:
      - "production"
      - "staging"
      - "canary"
    description: "The deployment target. Set to 'staging' by default."

job:
  script: echo 1

2. Navigate to -/pipelines/new and verify that your variables are output in the pipeline variables form.
3. update variables and click "New pipeline"

Related to #520831 (closed)

.gitlab/ci/rails/shared.gitlab-ci.yml

@@ -243,47 +243,11 @@ include:
     - .rspec-base
     - .use-pg14-es7-ee
 
-.rspec-ee-base-pg14-es8:
-  extends:
-    - .rspec-base
-    - .use-pg14-es8-ee
-    - .rails:rules:run-search-tests
-
-.rspec-ee-base-pg14-opensearch1:
-  extends:
-    - .rspec-base
-    - .use-pg14-opensearch1-ee
-    - .rails:rules:run-search-tests
-
-.rspec-ee-base-pg14-opensearch2:
-  extends:
-    - .rspec-base
-    - .use-pg14-opensearch2-ee
-    - .rails:rules:run-search-tests
-
 .rspec-ee-base-pg15:
   extends:
     - .rspec-base
     - .use-pg15-es7-ee
 
-.rspec-ee-base-pg15-es8:
-  extends:
-    - .rspec-base
-    - .use-pg15-es8-ee
-    - .rails:rules:run-search-tests
-
-.rspec-ee-base-pg15-opensearch1:
-  extends:
-    - .rspec-base
-    - .use-pg15-opensearch1-ee
-    - .rails:rules:run-search-tests
-
-.rspec-ee-base-pg15-opensearch2:
-  extends:
-    - .rspec-base
-    - .use-pg15-opensearch2-ee
-    - .rails:rules:run-search-tests
-
 .rspec-ee-base-pg16:
   extends:
     - .rspec-base