Remove instrumented test dependencies

The server is not a real Android application, it's just a jar with a
main method. Instrumented tests are meaningless in this context.

server/build.gradle

@@ -21,6 +21,4 @@ android {
 dependencies {
     implementation fileTree(dir: 'libs', include: ['*.jar'])
     testImplementation 'junit:junit:4.12'
-    androidTestImplementation 'com.android.support.test:runner:1.0.1'
-    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
 }