recovery_ui: Remove RecoveryUI::last_key.

It's a private member, and the last user has been removed in [1] in
2015.

[1] commit ec28340cf3af1029a00db1c83d78d14e8798e245,
https://android-review.googlesource.com/c/platform/bootable/recovery/+/146330

Test: mmma -j bootable/recovery
Change-Id: I65a2370cb20a7b296888425a44a42c8b90abc766
diff --git a/recovery_ui/include/recovery_ui/ui.h b/recovery_ui/include/recovery_ui/ui.h
index 797e2f0..d2ebad2 100644
--- a/recovery_ui/include/recovery_ui/ui.h
+++ b/recovery_ui/include/recovery_ui/ui.h
@@ -230,6 +230,7 @@
 
   bool InitScreensaver();
   void SetScreensaverState(ScreensaverState state);
+
   // Key event input queue
   std::mutex key_queue_mutex;
   std::condition_variable key_queue_cond;
@@ -243,7 +244,6 @@
   int rel_sum;
 
   int consecutive_power_keys;
-  int last_key;
 
   bool has_power_key;
   bool has_up_key;
diff --git a/recovery_ui/ui.cpp b/recovery_ui/ui.cpp
index cf0d3b5..1f1cd18 100644
--- a/recovery_ui/ui.cpp
+++ b/recovery_ui/ui.cpp
@@ -70,7 +70,6 @@
       key_down_count(0),
       enable_reboot(true),
       consecutive_power_keys(0),
-      last_key(-1),
       has_power_key(false),
       has_up_key(false),
       has_down_key(false),
@@ -585,7 +584,6 @@
     consecutive_power_keys = 0;
   }
 
-  last_key = key;
   return (IsTextVisible() || screensaver_state_ == ScreensaverState::OFF) ? ENQUEUE : IGNORE;
 }