installd: Simplify Dalvik cache path creation

Installd computes Dalvik cache path for a dex file by concatenating
'/classes.dex' to the APKs absolute path and then replacing all '/'
characters with '@'. OTA preopt does the same, only in reverse order,
i.e by concatenating '@classes.dex' to altered absolute path.

This patch unifies the two approaches so as to keep only one string
constant.

Change-Id: I69bb6bca831f45c873a0eb8580cf8d4b011f3b09
diff --git a/cmds/installd/installd_constants.h b/cmds/installd/installd_constants.h
index 8513695..dfde727 100644
--- a/cmds/installd/installd_constants.h
+++ b/cmds/installd/installd_constants.h
@@ -49,8 +49,7 @@
 
 // This is used as a string literal, can't be constants. TODO: std::string...
 #define DALVIK_CACHE "dalvik-cache"
-constexpr const char* DALVIK_CACHE_POSTFIX = "/classes.dex";
-constexpr const char* DALVIK_CACHE_POSTFIX2 = "@classes.dex";
+constexpr const char* DALVIK_CACHE_POSTFIX = "@classes.dex";
 
 constexpr const char* IDMAP_PREFIX = "/data/resource-cache/";
 constexpr const char* IDMAP_SUFFIX = "@idmap";