Remove unnecessary CI script.

Now that there's a single top level gradle project, we don't need any of
this. The new thing is actually more thorough, because it'll build all
build types of each sample instead of just debug, which is quite
important for things like the sanitizer sample.

#1010

.github/workflows/build.yml

@@ -23,9 +23,7 @@ jobs:
 
     - name: build samples
       run: |
-        export SAMPLE_CI_RESULT=0
-        source .ci_tools/build_samples.sh
-        eval "[[ $SAMPLE_CI_RESULT == 0 ]]"
+        ./gradlew build
 
     - uses: pre-commit/[email protected]