Revert "Remove Array.count, it is redundant with protocol extensions"

This reverts commit r28247 while we discuss the change.

Swift SVN r28292

stdlib/public/core/SequenceAlgorithms.swift.gyb

@@ -342,7 +342,7 @@ extension SequenceType {
     // optimized to a memcpy() sometimes.  Those cases are usually collections,
     // though.
     var result = Array(self)
-    let count = result.count()
+    let count = result.count
     for i in 0..<count/2 {
       swap(&result[i], &result[count - i - 1])
     }