Tools: move removal of modemmanager down

... so it doesn't get reinstalled later

Tools/environment_install/install-prereqs-ubuntu.sh

@@ -154,14 +154,6 @@ echo "$sep"
 sudo usermod -a -G dialout $USER
 echo "Done!"
 
-echo "$sep"
-echo "Removing modemmanager package that could conflict with firmware uploading"
-echo "$sep"
-if package_is_installed "modemmanager" -eq 1; then
-    $APT_GET remove modemmanager
-fi
-echo "Done!"
-
 # Add back python symlink to python interpreter on Ubuntu >= 20.04
 if [ ${RELEASE_CODENAME} == 'focal' ]; then
     BASE_PKGS+=" python-is-python3"
@@ -204,6 +196,14 @@ if [[ -z "${DO_AP_STM_ENV}" ]] && maybe_prompt_user "Install ArduPilot STM32 too
     DO_AP_STM_ENV=1
 fi
 
+echo "$sep"
+echo "Removing modemmanager package that could conflict with firmware uploading"
+echo "$sep"
+if package_is_installed "modemmanager" -eq 1; then
+    $APT_GET remove modemmanager
+fi
+echo "Done!"
+
 CCACHE_PATH=$(which ccache)
 if [[ $DO_AP_STM_ENV -eq 1 ]]; then
   install_arm_none_eabi_toolchain