ci: Drop unnecessary outer stage

We define stages inside of this stage, so get rid of the outer `FCOS`
stage. This should help rendering the pipeline in BlueOcean more
clearly.

.cci.jenkinsfile

@@ -42,7 +42,6 @@ stage("Build") {
 
 // Build FCOS and run kola tests.
 // Both fcosKola and fcosKolaTestIso require 4G max. Add 512M for overhead.
-stage("FCOS") {
 cosaPod(runAsUser: 0, memory: "4608Mi", cpu: "4") {
   stage("Build FCOS") {
     checkout scm
@@ -67,4 +66,3 @@ stage("FCOS") {
   fcosKola(cosaDir: "${env.WORKSPACE}")
   fcosKolaTestIso(cosaDir: "${env.WORKSPACE}", skipMetal4k: true, skipMultipath: true)
 }
-}