tests: Use get_bootloader_message_blk_device() to find /misc.

Since commit fb00d82f32 has added
get_bootloader_message_blk_device() as an API, switch the tests-local
implementation to it.

Test: recovery_component_test on angler.
Test: recovery_component_test on a local build that doesn't have /misc.
Change-Id: I4f5f542cb9ef58292c587a677da73d8822db7262

tests/component/bootloader_message_test.cpp

@@ -21,14 +21,13 @@
 #include <bootloader_message/bootloader_message.h>
 #include <gtest/gtest.h>
 
-#include "common/component_test_util.h"
-
 class BootloaderMessageTest : public ::testing::Test {
  protected:
   BootloaderMessageTest() : has_misc(true) {}
 
   virtual void SetUp() override {
-    has_misc = parse_misc();
+    std::string err;
+    has_misc = !get_bootloader_message_blk_device(&err).empty();
   }
 
   virtual void TearDown() override {