[Build] Remove workaround for previously different default shell

On the new Ubuntu images initially the 'dash' shell was used by default
and now it was changed to use 'bash' again.

So we don't have to explicitly specify the shell anymore.

See https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/issues/5061

Jenkinsfile

@@ -25,7 +25,7 @@ pipeline {
 					string(credentialsId: 'gpg-passphrase', variable: 'KEYRING_PASSPHRASE')
 				]) {
 				xvnc(useXauthority: true) {
-					sh '''#!/bin/bash -x
+					sh '''
 						mavenArgs="clean verify --batch-mode -Dmaven.test.failure.ignore=true -Dtycho.p2.baselineMode=failCommon"
 						if [[ ${BRANCH_NAME} == master ]] || [[ ${BRANCH_NAME} =~ m2e-[0-9]+\\.[0-9]+\\.x ]]; then
 							mvn ${mavenArgs} -Peclipse-sign,its -Dtycho.pgp.signer.bc.secretKeys="${KEYRING}" -Dgpg.passphrase="${KEYRING_PASSPHRASE}"
@@ -54,7 +54,7 @@ pipeline {
 			}
 			steps {
 				sshagent(['projects-storage.eclipse.org-bot-ssh']) {
-					sh '''#!/bin/bash -x
+					sh '''
 						deployM2ERepository()
 						{
 							echo Deploy m2e repo to ${1}