Fix pattern rules for $(installed_odex) for libdvm.

When the VM is libdvm, we don't put the odex files in an arch specific
subdirectory. The previous pattern rules don't work because of the extra
"/". With this change, % evaluates to empty string when it's built for
libdvm; % evaluates to "<arch_name>/" when it's built for libart.
Also removed use of $(create-empty-package), which may causes file name
(dummy) conflict with the rule of package.apk.

Bug: 15311527

(cherry picked from commit 994c226b)

Change-Id: I5469ef1994f2ba91a9c25126349156752fc35b4b