fix(ci): properly removing docker volumes

Laurent noticed it on one of his MR and confirmed with him:
  -- Volumes have be created the 1st time they ran on avra on July 7th
  -- Volumes were created with not only the raw files but also the nr-softmodem executable

Solution: two-fold:
  1. using the `docker-compose down -v` syntax, the volume is deleted automatically
  2. I added redundancy with the custom command to remove the used volume

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

ci-scripts/xml_files/container_5g_rfsim_fdd_phytest.xml

@@ -28,6 +28,7 @@
         <TestCaseRequestedList>
  111111
  100011
+ 004000
  000010
  000011
  020011
@@ -45,6 +46,13 @@
                 <images_to_pull>oai-gnb oai-nr-ue</images_to_pull>
         </testCase>
 
+        <testCase id="004000">
+            <class>Custom_Command</class>
+            <desc>Clean-Up any residual volume</desc>
+            <node>localhost</node>
+            <command>docker volume rm 5g_rfsimulator_fdd_phytest_rrc.config</command>
+        </testCase>
+
         <testCase id="000010">
                 <class>DeployGenObject</class>
                 <desc>Deploy OAI 5G gNB RF sim SA</desc>