[REFACTOR] DynamicPartitionControl: minimize API

- Move UpdatePartitionMetadata in boot_control_android.cc to
  DynamicPartitionControlAndroid::PreparePartitionsForUpdate to
  reflect code ownership better.
- Minimize the API by removing unused functions now that we have
  PreparePartitionsForUpdate
- Fix tests: replace MockDynamicPartitionControl to
  MockDynamicPartitionControlAndroid because it tests
  DynamicPartitionControlAndroid.

Test: unit test
Test: manually apply full OTA
Change-Id: I2959270bd89c4f8ddaa45cf45ba93acdec850f67
diff --git a/Android.bp b/Android.bp
index de4d3b3..fab5d27 100644
--- a/Android.bp
+++ b/Android.bp
@@ -214,6 +214,7 @@
     srcs: [
         "boot_control_android.cc",
         "dynamic_partition_control_android.cc",
+        "dynamic_partition_utils.cc",
     ],
 }