Remove an unused command line flag.

--enable_ambiguity_expansion flag has been enabled by default
in production.  We don't need to keep it configurable.

BUG=none
TEST=unittest
diff --git a/src/mozc_version_template.txt b/src/mozc_version_template.txt
index 52645ee..afe149a 100644
--- a/src/mozc_version_template.txt
+++ b/src/mozc_version_template.txt
@@ -1,6 +1,6 @@
 MAJOR=2
 MINOR=17
-BUILD=2092
+BUILD=2093
 REVISION=102
 # NACL_DICTIONARY_VERSION is the target version of the system dictionary to be
 # downloaded by NaCl Mozc.
diff --git a/src/prediction/predictor.cc b/src/prediction/predictor.cc
index 1e816d3..bf97296 100644
--- a/src/prediction/predictor.cc
+++ b/src/prediction/predictor.cc
@@ -39,9 +39,6 @@
 #include "converter/segments.h"
 #include "session/commands.pb.h"
 
-// TODO(team): Implement ambiguity expansion for rewriters.
-DEFINE_bool(enable_ambiguity_expansion, true,
-            "Enable ambiguity trigger expansion for predictions");
 DECLARE_bool(enable_expansion_for_dictionary_predictor);
 DECLARE_bool(enable_expansion_for_user_history_predictor);
 
@@ -75,10 +72,10 @@
       user_history_predictor_(user_history_predictor) {
   DCHECK(dictionary_predictor_.get());
   DCHECK(user_history_predictor_.get());
-  FLAGS_enable_expansion_for_dictionary_predictor =
-      FLAGS_enable_ambiguity_expansion;
-  FLAGS_enable_expansion_for_user_history_predictor =
-      FLAGS_enable_ambiguity_expansion;
+  // TODO(noriyukit): Now the following features are stable, so remove these
+  // flags.
+  FLAGS_enable_expansion_for_dictionary_predictor = true;
+  FLAGS_enable_expansion_for_user_history_predictor = true;
 }
 
 BasePredictor::~BasePredictor() {}