Drop CentOS 7 changes for Ruby building

https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/8097
dropped support for CentOS 7, but
https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/8087 was
merged right after that. Drop the CentOS 7 conditional to
fix things.

config/software/ruby.rb

@@ -90,9 +90,9 @@ env['CFLAGS'] << ' -O3 -g -pipe'
 # Workaround for https://bugs.ruby-lang.org/issues/19161
 env['CFLAGS'] << ' -std=gnu99' if OhaiHelper.os_platform == 'sles'
-# We need to recompile native gems on SLES 12 and CentOS 7 because
-# precompiled gems such as nokogiri now require glibc >= 2.29,
-# and these operating systems use older versions.
+# We need to recompile native gems on SLES 12 because precompiled gems
+# such as nokogiri now require glibc >= 2.29, and SLES 12 uses an older
+# version.
 #
 # By default, Ruby C extensions use `RbConfig::MAKEFILE_CONFIG["CC"]`,
 # which is the C compiler used to build Ruby. Some C extensions can use
@@ -102,10 +102,7 @@ env['CFLAGS'] << ' -std=gnu99' if OhaiHelper.os_platform == 'sles'
 # support. For now, compiling the Ruby interpreter with GCC 8 works and
 # avoids the need to specify the compiler for every extension that needs
 # it.
-if OhaiHelper.centos7?
-  env['CC'] = "/opt/rh/devtoolset-8/root/usr/bin/gcc"
-  env['CXX'] = "/opt/rh/devtoolset-8/root/usr/bin/g++"
-elsif OhaiHelper.sles12?
+if OhaiHelper.sles12?
   env['CC'] = "/usr/bin/gcc-8"
   env['CXX'] = "/usr/bin/g++-8"
 end