AAPT2: Clean up tests a bit

Since the latest gtest has fixed support for
explicit bool operators, remvoe AAPT_ASSERT_* and AAPT_EXPECT_*.

Also switch to use NotNull() matchers, which are more legible.

Test: make aapt2_tests
Change-Id: Idce199ca9d567d70f7aae275fee15e04bb914c9e
diff --git a/tools/aapt2/test/Builders.h b/tools/aapt2/test/Builders.h
index f3da780..6b82076 100644
--- a/tools/aapt2/test/Builders.h
+++ b/tools/aapt2/test/Builders.h
@@ -212,8 +212,7 @@
   }
 
   StyleBuilder& AddItem(const android::StringPiece& str, std::unique_ptr<Item> value) {
-    style_->entries.push_back(
-        Style::Entry{Reference(ParseNameOrDie(str)), std::move(value)});
+    style_->entries.push_back(Style::Entry{Reference(ParseNameOrDie(str)), std::move(value)});
     return *this;
   }
 
@@ -224,7 +223,9 @@
     return *this;
   }
 
-  std::unique_ptr<Style> Build() { return std::move(style_); }
+  std::unique_ptr<Style> Build() {
+    return std::move(style_);
+  }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(StyleBuilder);