As it currently stands there isn't much, if anything, you can do here.  The Marketing Cloud SDK compiles the tozny library into the distributed aar rather than declaring it in the pom file distributed.  This is done because there are certain modifications made to the code required by the SDK.  Because of this, adding an exclude dependency declaration to your build.gradle file will not have the desired effect.  

I'll open a ticket to get this addressed in the SDK.