[ALOY-751] Android: some Style properties are not removed using $.removeClass

Problem description

Using Dynamic Styling, not all styles properties seems to be correctly removed on Android when using $.removeClass unless they have a value and is different from null

Steps to reproduce

1. Run https://github.com/appcelerator/alloy/tree/master/test/apps/advanced/dynamic_styling on Android emulator or device 2. Check the 'Add/Remove Classes' example. Result: class styles are correctly added to 'test label 1', however when removing them, the 'backgroundColor' and 'borderRadius' properties from the '.redbg' class are still applied ('color' property, also defined in the .redbg class, is correctly removed) On iOS it works as expected. 3. Modify the '.medium' class included in 'classes.tss', changing backgroundColor value from null to something else and adding a borderRadius value different from null ex:

'.medium': {
	font: {
		fontSize: '24dp',
		fontWeight: 'bold'
	},
	backgroundColor: 'orange',
	borderRadius:0,
	height: null,
	width: null
}

Result: in this case it works as expected - when removing the class, backgroundColor is back to 'orange' value and borderRadius is back to '0'. Note that height and weight values behave correctly also if set to null.