Remove last using directives from global header scope

Bug: None
Test: Compiles, unittests pass

Change-Id: I66dee2504b28049ecb74526a08345e999d57db8d
diff --git a/type_java.cpp b/type_java.cpp
index f056610..b792ba7 100644
--- a/type_java.cpp
+++ b/type_java.cpp
@@ -23,6 +23,7 @@
 #include "aidl_language.h"
 #include "logging.h"
 
+using std::string;
 using android::base::Split;
 using android::base::Join;
 using android::base::Trim;