EMQX: removal logic in emqx update (#8050)

Added conditional checks to remove either emqx or emqx-enterprise packages.

ct/emqx.sh

@@ -31,7 +31,13 @@ function update_script() {
     msg_ok "Stopped EMQX"
 
     msg_info "Removing old EMQX"
+    if dpkg -l | grep -q "^ii\s\+emqx\s"; then
       $STD apt-get remove --purge -y emqx
+    elif dpkg -l | grep -q "^ii\s\+emqx-enterprise\s"; then
+      $STD apt-get remove --purge -y emqx-enterprise
+    else
+      msg_ok "No old EMQX package found"
+    fi
     msg_ok "Removed old EMQX"
 
     msg_info "Downloading EMQX v${RELEASE}"