It could be a workaround to delete the gdal modules manually.
They are named:
org-esa-s2tbx-s2tbx-gdal-reader.jar and org-esa-s2tbx-s2tbx-gdal-reader-ui.jar
You can find them either in
C:\Users\USER_NAME\AppData\Roaming\SNAP\modules
or on Unix
/home/USER_NAME/.snap/system/modules
Delete both files.
After starting SNAP you will be asked that if you want to disable these modules. Answer yes.