Rename gpg pashprase env variable for maven

Fixes warnings :
```
12:37:46  [WARNING]  Parameter 'passphrase' (user property
'gpg.passphrase') is deprecated: Do not use this configuration, it may
leak sensitive information. Rely on gpg-agent or env variables instead.
12:37:46  [WARNING]
12:37:46  [WARNING] W A R N I N G
12:37:46  [WARNING]
12:37:46  [WARNING] Do not store passphrase in any file (disk or SCM
repository),
12:37:46  [WARNING] instead rely on GnuPG agent or provide passphrase in
12:37:46  [WARNING] MAVEN_GPG_PASSPHRASE environment variable for batch
mode.
12:37:46  [WARNING]
12:37:46  [WARNING] Sensitive content loaded from Mojo configuration
```

from I-builds.
Rename is being done only for this step to get rid of the warning as for
the other steps it's not a maven env variable (thus shouldn't be named
like that) and will require changing multiple scripts.

JenkinsJobs/Builds/I_build.groovy

@@ -247,7 +247,7 @@ spec:
 	  stage('Aggregator maven build'){
 	      environment {
                 KEYRING = credentials('secret-subkeys-releng.asc')
-                KEYRING_PASSPHRASE = credentials('secret-subkeys-releng.acs-passphrase')
+                MAVEN_GPG_PASSPHRASE = credentials('secret-subkeys-releng.acs-passphrase')
           }
           steps {
               container('jnlp') {

cje-production/mbscripts/mb220_buildSdkPatch.sh

@@ -43,7 +43,6 @@ mvn clean verify -DskipTests=true ${MVN_ARGS} \
   -DbuildType=$BUILD_TYPE \
   -DbuildId=$BUILD_ID \
   -Declipse-p2-repo.url=NOT_FOR_PRODUCTION_USE \
-  -Dgpg.passphrase=${KEYRING_PASSPHRASE} \
   -Dcbi-ecj-version=99.99 \
   -e \
   -T 1C \