[CI] Test SGX remote attestation examples on Ubuntu 18.04 and 20.04

Previously, it was tested only on Ubuntu 18.04 (bionic) due to concerns
over sending too many EPID requests to the Intel Attestation Service
(IAS). This shouldn't be an issue anymore.

Signed-off-by: Dmitrii Kuvaiskii <dmitrii.kuvaiskii@intel.com>

.ci/lib/stage-test-sgx.jenkinsfile

@@ -103,9 +103,6 @@ stage('test-sgx') {
     }
     timeout(time: 5, unit: 'MINUTES') {
         sh '''
-            # test SGX remote attestation only on Ubuntu 18.04 to keep internet requests to minimum
-            .ci/isdistro bionic || exit 0
-
             cd Examples/ra-tls-mbedtls
             if [ "${ra_client_spid}" != "" ] && [ "${ra_client_key}" != "" ]; \
             then \
@@ -123,9 +120,6 @@ stage('test-sgx') {
     }
     timeout(time: 5, unit: 'MINUTES') {
         sh '''
-            # test SGX remote attestation only on Ubuntu 18.04 to keep internet requests to minimum
-            .ci/isdistro bionic || exit 0
-
             cd Examples/ra-tls-secret-prov
             if [ "${ra_client_spid}" != "" ] && [ "${ra_client_key}" != "" ]; \
             then \