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/util/Maybe_test.cpp b/tools/aapt2/util/Maybe_test.cpp
index ca14793..2057ddc 100644
--- a/tools/aapt2/util/Maybe_test.cpp
+++ b/tools/aapt2/util/Maybe_test.cpp
@@ -80,22 +80,22 @@
 
 TEST(MaybeTest, MakeNothing) {
   Maybe<int> val = make_nothing<int>();
-  AAPT_EXPECT_FALSE(val);
+  EXPECT_FALSE(val);
 
   Maybe<std::string> val2 = make_nothing<std::string>();
-  AAPT_EXPECT_FALSE(val2);
+  EXPECT_FALSE(val2);
 
   val2 = make_nothing<std::string>();
-  AAPT_EXPECT_FALSE(val2);
+  EXPECT_FALSE(val2);
 }
 
 TEST(MaybeTest, MakeSomething) {
   Maybe<int> val = make_value(23);
-  AAPT_ASSERT_TRUE(val);
+  ASSERT_TRUE(val);
   EXPECT_EQ(23, val.value());
 
   Maybe<std::string> val2 = make_value(std::string("hey"));
-  AAPT_ASSERT_TRUE(val2);
+  ASSERT_TRUE(val2);
   EXPECT_EQ(std::string("hey"), val2.value());
 }