Revert the default setting of InitFromCmdLineArgs().

Summary:
Revert the default setting of InitFromCmdLineArgs() as all the callers
currently provide full set of arguments.

Test Plan:
make reduce_levels_test
./reduce_levels_test

Reviewers: haobo, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19257

util/ldb_cmd.h

@@ -55,15 +55,15 @@ public:
 
   static LDBCommand* InitFromCmdLineArgs(
     const vector<string>& args,
-    const Options& options = Options(),
+    const Options& options,
-    const LDBOptions& ldb_options = LDBOptions()
+    const LDBOptions& ldb_options
   );
 
   static LDBCommand* InitFromCmdLineArgs(
     int argc,
     char** argv,
-    const Options& options = Options(),
+    const Options& options,
-    const LDBOptions& ldb_options = LDBOptions()
+    const LDBOptions& ldb_options
   );
 
   bool ValidateCmdLineOptions();