[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/boot_control_android_unittest.cc b/boot_control_android_unittest.cc
index 94e195f..dfcb6fb 100644
--- a/boot_control_android_unittest.cc
+++ b/boot_control_android_unittest.cc
@@ -262,7 +262,7 @@
     // Fake init bootctl_
     bootctl_.module_ = new NiceMock<MockBootControlHal>();
     bootctl_.dynamic_control_ =
-        std::make_unique<NiceMock<MockDynamicPartitionControl>>();
+        std::make_unique<NiceMock<MockDynamicPartitionControlAndroid>>();
 
     ON_CALL(module(), getNumberSlots()).WillByDefault(Invoke([] {
       return kMaxNumSlots;
@@ -297,8 +297,8 @@
   }
 
   // Return the mocked DynamicPartitionControlInterface.
-  NiceMock<MockDynamicPartitionControl>& dynamicControl() {
-    return static_cast<NiceMock<MockDynamicPartitionControl>&>(
+  NiceMock<MockDynamicPartitionControlAndroid>& dynamicControl() {
+    return static_cast<NiceMock<MockDynamicPartitionControlAndroid>&>(
         *bootctl_.dynamic_control_);
   }