Replace Maybe with std::optional

With c++17, std::optional provides the functionality that Maybe
provided.

Bug: 183215655
Test: aapt2_tests
Change-Id: I62bb9c2fa4985dc5217a6ed153df92b85ad9a034
diff --git a/tools/aapt2/test/Common.cpp b/tools/aapt2/test/Common.cpp
index 23c2218..e029d02 100644
--- a/tools/aapt2/test/Common.cpp
+++ b/tools/aapt2/test/Common.cpp
@@ -48,7 +48,7 @@
                                           const android::StringPiece& res_name,
                                           const ConfigDescription& config,
                                           const android::StringPiece& product) {
-  Maybe<ResourceTable::SearchResult> result = table->FindResource(ParseNameOrDie(res_name));
+  std::optional<ResourceTable::SearchResult> result = table->FindResource(ParseNameOrDie(res_name));
   if (result) {
     ResourceConfigValue* config_value = result.value().entry->FindValue(config, product);
     if (config_value) {