Fix stacks on 64 bit processes.

debuggerd64 doesn't exist anymore, `debuggerd $PID` works on both 32
and 64 bit processes.

Bug: http://b/35872661
Change-Id: I47be05c7ec346e5d657d06e6c3aff1723494639b

envsetup.sh

@@ -1148,8 +1148,7 @@ function stacks()
             adb shell cat $TMP
         else
             # Dump stacks of native process
-            local USE64BIT="$(is64bit $PID)"
+            adb shell debuggerd -b $PID
-            adb shell debuggerd$USE64BIT -b $PID
         fi
     fi
 }