Remove __INTRODUCED_IN_FUTURE.

This hasn't been particularly useful, we haven't used it consistently,
and it has caused trouble.

Test: builds
Change-Id: Ic5b5b5124af98aa8301e602fd75b0eb72a5fc7f6
diff --git a/tools/versioner/src/DeclarationDatabase.h b/tools/versioner/src/DeclarationDatabase.h
index 0daa2cd..4496ee9 100644
--- a/tools/versioner/src/DeclarationDatabase.h
+++ b/tools/versioner/src/DeclarationDatabase.h
@@ -42,13 +42,12 @@
 };
 
 struct AvailabilityValues {
-  bool future = false;
   int introduced = 0;
   int deprecated = 0;
   int obsoleted = 0;
 
   bool empty() const {
-    return !(future || introduced || deprecated || obsoleted);
+    return !(introduced || deprecated || obsoleted);
   }
 
   bool operator==(const AvailabilityValues& rhs) const {