Do not obfuscate code (#39)

The app is open-source, so there is no point in obfuscating.
This change makes it easier to compare the distributed apk with
the source code. Proguard still removes unused elements.

Co-authored-by: Jakob Möller <jakob.moeller@sap.com>

Corona-Warn-App/proguard-rules.pro

@@ -24,7 +24,7 @@
 # debugging stack traces.
 -keepattributes SourceFile,LineNumberTable
 
-#-dontobfuscate
+-dontobfuscate
 # If you keep the line number information, uncomment this to
 # hide the original source file name.
 #-renamesourcefileattribute SourceFile