Nuke the CollectionType implementation from _BitMap.

It is dead code.

Swift SVN r32249

stdlib/public/core/HashedCollections.swift.gyb

@@ -1592,7 +1592,7 @@ collections = [
 }%
 
 /// A wrapper around a bitmap storage with room for at least bitCount bits.
-internal struct _BitMap : CollectionType {
+internal struct _BitMap {
   internal let values: UnsafeMutablePointer<UInt>
   internal let bitCount: Int
 
@@ -1630,20 +1630,6 @@ internal struct _BitMap : CollectionType {
     }
   }
 
-  internal var startIndex: Int {
-    @warn_unused_result
-    get {
-      return 0
-    }
-  }
-
-  internal var endIndex: Int {
-    @warn_unused_result
-    get {
-      return bitCount
-    }
-  }
-
   internal subscript(i: Int) -> Bool {
     @warn_unused_result
     get {