Merge pull request open-mpi#12805 from wenduwan/remove_rhel7

ci: remove rhel7

Author: jsquyres

.ci/community-jenkins/Jenkinsfile

@@ -54,7 +54,7 @@ println('Tests Completed')
 def prepare_check_stages() {
     def configure_options = ["--disable-dlopen", "--disable-oshmem", "--enable-builtin-atomic", "--enable-ipv6"]
     def compilers = ["clang10", "gcc5", "gcc6", "gcc7", "gcc8", "gcc9", "gcc10"]
-    def platforms = ["amazon_linux_2", "amazon_linux_2-arm64", "rhel7", "rhel8", "ubuntu_18.04"]
+    def platforms = ["amazon_linux_2", "amazon_linux_2-arm64", "rhel8", "ubuntu_18.04"]
     def check_stages_list = []
 
     // Build everything stage