[TIMOB-18062] iOS: AttributedString Parity with Android

Jira: https://jira.appcelerator.org/browse/TIMOB-18062

This PR is a continuation of https://github.com/appcelerator/titanium_mobile/pull/6409/ which came from #6358.

It addresses the comments by @pingwang2011 for the Android portion of the code. The doc is still not completed yet as Titanium.UI.iOS.Attribute and Titanium.UI.iOS.AttributedString yml files are missing the "deprecated".

The propertyAccessors is now used in AttributedStringProxy.java, AttributeProxy.java and LabelProxy.java.
https://github.com/appcelerator/titanium_mobile/pull/6409#discussion-diff-21474987

Removed method:
"@Kroll.getProperty @Kroll.method
public AttributeProxy[] getAttributes()"
>From pingwang2011:
>Don't need this method if TiC.PROPERTY_ATTRIBUTES is added to propertyAccessors.

https://github.com/appcelerator/titanium_mobile/pull/6409#discussion-diff-21474991
Removed method:
"@Kroll.setProperty @Kroll.method
public void setAttributes(AttributeProxy[] values)"
>From pingwang2011
>Don't need this method if TiC.PROPERTY_ATTRIBUTES is added to propertyAccessors.