Disable DalvikVM GC logcat spam

Dalvik logs everytime a garbage collection is run. Disabled to remove
clutter from logcat. Can be renabled by #defining DEBUG.

Change-Id: I57a461857f8d0ecbf223f3c18187f62095adb5b4

Made minor changes to https://github.com/ParanoidAndroid/android_dalvik/commit/36ffd053900b25f46b6260f951852abbc49d5730

Re-enable GC logging by setting DALVIK_HEAP_DEBUG