Revert "csharp: Property Indexer implementation"
This reverts commit 0954e501fd4008c40b3848de1f2c91bcd53b2f71.
According to Framework Design Guidelines of MS, most of indexed properties are
not recommended in EFL#.
It is better to leave properties which have a key as methods.
Reviewers: woohyun, felipealmeida
Reviewed By: woohyun
Differential Revision: https://phab.enlightenment.org/D11114