Ensure ca.psiphon.aar is freshly created

The zip command alone updated contents of any existing ca.psiphon.aar,
which resulted in obsolete, omitted ABI files still being included in
the AAR.

MobileLibrary/Android/make.bash

@@ -120,6 +120,7 @@ fi
 cd -
 cd build-tmp/psi
 echo -e "-keep class psi.** { *; }\n"  >> proguard.txt
+rm -f ../../ca.psiphon.aar
 zip -r ../../ca.psiphon.aar ./
 cd -
 rm -rf build-tmp