Revert "Remove EXPAND/STRINGIFY macros."

This reverts commit ec9706738f35a859f66fd0758b73381055804f63.

Reason for revert: It's not a good idea to put RECOVERY_API_VERSION in
common.h, which might be included by device-specific codes (but with
RECOVERY_API_VERSION undefined).

Change-Id: I9feb9c64a5af3e9165164622a59b043aa28a8b8c
diff --git a/common.h b/common.h
index 87b8477..62fb132 100644
--- a/common.h
+++ b/common.h
@@ -22,8 +22,8 @@
 
 #include <string>
 
-static constexpr int kRecoveryApiVersion = RECOVERY_API_VERSION;  // Defined in Android.mk.
-static_assert(kRecoveryApiVersion >= 3, "Invalid recovery API version.");
+#define STRINGIFY(x) #x
+#define EXPAND(x) STRINGIFY(x)
 
 class RecoveryUI;