Update 0220-count-where.md (#2391)

* Update status (implemented).
* Add link to new implementation.
* Remove links to old implementations.

Author: benrimmington

proposals/0220-count-where.md

@@ -3,8 +3,8 @@
 * Proposal: [SE-0220](0220-count-where.md)
 * Author: [Soroush Khanlou](https://github.com/khanlou)
 * Review Manager: [Ben Cohen](https://github.com/airspeedswift)
-* Status: **Accepted**
-* Implementation: [apple/swift#16099](https://github.com/apple/swift/pull/16099), [apple/swift#22289](https://github.com/apple/swift/pull/22289) (revert PR)
+* Status: **Implemented (Swift 6.0)**
+* Implementation: [apple/swift#72705](https://github.com/apple/swift/pull/72705)
 * Review: ([first pitch](https://forums.swift.org/t/count-where-on-sequence/11186)) ([first review](https://forums.swift.org/t/se-0220-count-where/15048)) ([first acceptance](https://forums.swift.org/t/accepted-se-0220-count-where/15280)) ([second pitch](https://forums.swift.org/t/pitch-restore-count-where-from-se-0220/65859)) ([second review](https://forums.swift.org/t/refresh-review-se-0220-count-where/66235)) ([second acceptance](https://forums.swift.org/t/accepted-again-se-0220-count-where/66659))
 
 ## Introduction