Have metadata remove/free functions return void.

Only the unit tests were checking the return values of these functions.
The callers in actual code ignored their return values. So they can
just return void.

BUG=aomedia:2507

Change-Id: I9cdc3db52cae673fc6be440b912edc4de7d6aca0
diff --git a/test/metadata_test.cc b/test/metadata_test.cc
index 4bf9595..53aa429 100644
--- a/test/metadata_test.cc
+++ b/test/metadata_test.cc
@@ -101,7 +101,7 @@
   aom_metadata_t *metadata = aom_img_metadata_alloc(
       OBU_METADATA_TYPE_ITUT_T35, kExampleData, kExampleDataSize);
   ASSERT_NE(metadata, nullptr);
-  EXPECT_EQ(aom_img_metadata_free(metadata), 0);
+  aom_img_metadata_free(metadata);
 }
 
 TEST(MetadataTest, MetadataArrayAllocation) {
@@ -113,7 +113,7 @@
   metadata_array->metadata_array[1] = aom_img_metadata_alloc(
       OBU_METADATA_TYPE_ITUT_T35, kExampleData, kExampleDataSize);
 
-  EXPECT_EQ(aom_img_metadata_array_free(metadata_array), 2u);
+  aom_img_metadata_array_free(metadata_array);
 }
 
 TEST(MetadataTest, AddMetadataToImage) {
@@ -123,7 +123,7 @@
   ASSERT_EQ(aom_img_add_metadata(&image, OBU_METADATA_TYPE_ITUT_T35,
                                  kExampleData, kExampleDataSize),
             0);
-  EXPECT_EQ(aom_img_metadata_array_free(image.metadata), 1u);
+  aom_img_metadata_array_free(image.metadata);
   EXPECT_EQ(aom_img_add_metadata(NULL, OBU_METADATA_TYPE_ITUT_T35, kExampleData,
                                  kExampleDataSize),
             -1);
@@ -136,8 +136,8 @@
   ASSERT_EQ(aom_img_add_metadata(&image, OBU_METADATA_TYPE_ITUT_T35,
                                  kExampleData, kExampleDataSize),
             0);
-  EXPECT_EQ(aom_img_remove_metadata(&image), 1u);
-  EXPECT_EQ(aom_img_remove_metadata(NULL), 0u);
+  aom_img_remove_metadata(&image);
+  aom_img_remove_metadata(NULL);
 }
 
 TEST(MetadataTest, CopyMetadataToFrameBuffer) {
@@ -155,18 +155,18 @@
   EXPECT_EQ(status, 0);
   status = aom_copy_metadata_to_frame_buffer(NULL, metadata_array);
   EXPECT_EQ(status, -1);
-  EXPECT_EQ(aom_img_metadata_array_free(metadata_array), 1u);
+  aom_img_metadata_array_free(metadata_array);
 
   // Metadata_array_2
   aom_metadata_array_t *metadata_array_2 = aom_img_metadata_array_alloc(0);
   ASSERT_NE(metadata_array_2, nullptr);
   status = aom_copy_metadata_to_frame_buffer(&yvBuf, metadata_array_2);
   EXPECT_EQ(status, -1);
-  EXPECT_EQ(aom_img_metadata_array_free(metadata_array_2), 0u);
+  aom_img_metadata_array_free(metadata_array_2);
 
   // YV12_BUFFER_CONFIG
   status = aom_copy_metadata_to_frame_buffer(&yvBuf, NULL);
   EXPECT_EQ(status, -1);
-  EXPECT_EQ(aom_remove_metadata_from_frame_buffer(NULL), 0u);
-  EXPECT_EQ(aom_remove_metadata_from_frame_buffer(&yvBuf), 1u);
+  aom_remove_metadata_from_frame_buffer(&yvBuf);
+  aom_remove_metadata_from_frame_buffer(NULL);
 }