Move version constants back into modules so F-Droid can find them.

This reverts commit de9c6d44, except that the version numbers have
increased in the meantime.

build.gradle

@@ -33,12 +33,3 @@ buildscript {
 		classpath files('libs/gradle-witness.jar')
 	}
 }
-
-project.ext {
-	buildToolsVersion = '30.0.2'
-	compileSdkVersion = 30
-	minSdkVersion = 16
-	targetSdkVersion = 29
-	versionCode = 10213
-	versionName = '1.2.13'
-}