AAPT2: Remove usage of u16string

For legacy reasons, we kept around the use of UTF-16 internally
in AAPT2. We don't need this and this CL removes all instances of
std::u16string and StringPiece16. The only places still needed
are when interacting with the ResTable APIs that only operate in
UTF16.

Change-Id: I492475b84bb9014fa13bf992cff447ee7a5fe588
diff --git a/tools/aapt2/compile/IdAssigner_test.cpp b/tools/aapt2/compile/IdAssigner_test.cpp
index e25a17a..802e99a 100644
--- a/tools/aapt2/compile/IdAssigner_test.cpp
+++ b/tools/aapt2/compile/IdAssigner_test.cpp
@@ -27,10 +27,10 @@
 
 TEST(IdAssignerTest, AssignIds) {
     std::unique_ptr<ResourceTable> table = test::ResourceTableBuilder()
-            .addSimple(u"@android:attr/foo")
-            .addSimple(u"@android:attr/bar")
-            .addSimple(u"@android:id/foo")
-            .setPackageId(u"android", 0x01)
+            .addSimple("@android:attr/foo")
+            .addSimple("@android:attr/bar")
+            .addSimple("@android:id/foo")
+            .setPackageId("android", 0x01)
             .build();
 
     std::unique_ptr<IAaptContext> context = test::ContextBuilder().build();
@@ -42,12 +42,12 @@
 
 TEST(IdAssignerTest, AssignIdsWithReservedIds) {
     std::unique_ptr<ResourceTable> table = test::ResourceTableBuilder()
-            .addSimple(u"@android:attr/foo", ResourceId(0x01040006))
-            .addSimple(u"@android:attr/bar")
-            .addSimple(u"@android:id/foo")
-            .addSimple(u"@app:id/biz")
-            .setPackageId(u"android", 0x01)
-            .setPackageId(u"app", 0x7f)
+            .addSimple("@android:attr/foo", ResourceId(0x01040006))
+            .addSimple("@android:attr/bar")
+            .addSimple("@android:id/foo")
+            .addSimple("@app:id/biz")
+            .setPackageId("android", 0x01)
+            .setPackageId("app", 0x7f)
             .build();
 
     std::unique_ptr<IAaptContext> context = test::ContextBuilder().build();
@@ -59,10 +59,10 @@
 
 TEST(IdAssignerTest, FailWhenNonUniqueIdsAssigned) {
     std::unique_ptr<ResourceTable> table = test::ResourceTableBuilder()
-            .addSimple(u"@android:attr/foo", ResourceId(0x01040006))
-            .addSimple(u"@android:attr/bar", ResourceId(0x01040006))
-            .setPackageId(u"android", 0x01)
-            .setPackageId(u"app", 0x7f)
+            .addSimple("@android:attr/foo", ResourceId(0x01040006))
+            .addSimple("@android:attr/bar", ResourceId(0x01040006))
+            .setPackageId("android", 0x01)
+            .setPackageId("app", 0x7f)
             .build();
 
     std::unique_ptr<IAaptContext> context = test::ContextBuilder().build();