Disable proguard optimization when not using jack

Proguard optimization causes errors when used with dx:
warning: Ignoring InnerClasses attribute for an anonymous inner class
(android.support.transition.ViewGroupUtilsApi14$1) that doesn't come with an
associated EnclosingMethod attribute. This class was probably produced by a
compiler that did not target the modern .class file format. The recommended
solution is to recompile the class from source, using an up-to-date compiler
and without specifying any "-target" type options. The consequence of ignoring
this warning is that reflective operations on this class will incorrectly
indicate that it is *not* an inner class.
...
Uncaught translation error: com.android.dx.cf.code.SimException: local variable type mismatch: attempt to set or access a value of type android.service.notification.StatusBarNotification[] using a local variable of type java.lang.String. This is symptomatic of .class transformation tools that ignore local variable information.
Uncaught translation error: com.android.dx.cf.code.SimException: local variable type mismatch: attempt to set or access a value of type com.google.common.collect.SingletonImmutableList using a local variable of type java.lang.Object[]. This is symptomatic of .class transformation tools that ignore local variable information.

Bug: 37077388
Test: m -j ANDROID_COMPILE_WITH_JACK=false
Change-Id: I687fff179c9d264f788e89e18cf5875c5f0663fc