[skip e2e] remove image repo in jenkinsfile (#13822)

Signed-off-by: NJenny Li <jing.li@zilliz.com>

build/ci/jenkins/Nightly.groovy

@@ -34,7 +34,6 @@ pipeline {
     environment {
         PROJECT_NAME = "milvus"
         SEMVER = "${BRANCH_NAME.contains('/') ? BRANCH_NAME.substring(BRANCH_NAME.lastIndexOf('/') + 1) : BRANCH_NAME}"
-        IMAGE_REPO = "dockerhub-mirror-sh.zilliz.cc/milvusdb"
         DOCKER_BUILDKIT = 1
         ARTIFACTS = "${env.WORKSPACE}/_artifacts"
         DOCKER_CREDENTIALS_ID = "f0aacc8e-33f2-458a-ba9e-2c44f431b4d2"

build/ci/jenkins/PR.groovy

@@ -27,7 +27,6 @@ pipeline {
     environment {
         PROJECT_NAME = 'milvus'
         SEMVER = "${BRANCH_NAME.contains('/') ? BRANCH_NAME.substring(BRANCH_NAME.lastIndexOf('/') + 1) : BRANCH_NAME}"
-        IMAGE_REPO = 'dockerhub-mirror-sh.zilliz.cc/milvusdb'
         DOCKER_BUILDKIT = 1
         ARTIFACTS = "${env.WORKSPACE}/_artifacts"
         DOCKER_CREDENTIALS_ID = "f0aacc8e-33f2-458a-ba9e-2c44f431b4d2"

build/ci/jenkins/PublishImages.groovy

@@ -20,7 +20,6 @@ pipeline {
     }
 
     environment {
-        IMAGE_REPO = "dockerhub-mirror-sh.zilliz.cc/milvusdb"
         DOCKER_CREDENTIALS_ID = "f0aacc8e-33f2-458a-ba9e-2c44f431b4d2"
         TARGET_REPO = "milvusdb"
         HARBOR_CREDENTIAL_ID = "harbor-zilliz-cc-registry"