[Swift] Remove Triple.swift.

This is not in use.  It never has been, as far as I can see.

runtime/Swift/Sources/Antlr4/misc/Triple.swift

@@ -1,38 +0,0 @@
-/// 
-/// Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
-/// Use of this file is governed by the BSD 3-clause license that
-/// can be found in the LICENSE.txt file in the project root.
-///
-
-
-public class Triple<A:Hashable, B:Hashable, C:Hashable>: Hashable, CustomStringConvertible {
-    public let a: A
-    public let b: B
-    public let c: C
-
-    public init(_ a: A, _ b: B, _ c: C) {
-        self.a = a
-        self.b = b
-        self.c = c
-    }
-    public var hashValue: Int {
-        var hash = MurmurHash.initialize()
-        hash = MurmurHash.update(hash, a)
-        hash = MurmurHash.update(hash, b)
-        hash = MurmurHash.update(hash, c)
-        return MurmurHash.finish(hash, 3)
-    }
-
-
-    public var description: String {
-        return "\(a),\(b),(c)"
-    }
-}
-
-public func ==<A, B, C>(lhs: Triple<A, B, C>, rhs: Triple<A, B, C>) -> Bool {
-    if lhs === rhs {
-        return true
-    }
-    // return false
-    return lhs.a == rhs.a && lhs.b == rhs.b && lhs.c == rhs.c
-}