Remove some unused functions and methods

In the case of CKey's destructor, it seems to have been an oversight in
f4d1fc259 not to delete it. At this point, it results in the move
constructors/assignment operators for CKey being deleted, which may have
a performance impact.

src/hash.h

@@ -88,20 +88,6 @@ inline uint256 Hash(const T1 p1begin, const T1 p1end,
     return result;
 }
 
-/** Compute the 256-bit hash of the concatenation of three objects. */
-template<typename T1, typename T2, typename T3>
-inline uint256 Hash(const T1 p1begin, const T1 p1end,
-                    const T2 p2begin, const T2 p2end,
-                    const T3 p3begin, const T3 p3end) {
-    static const unsigned char pblank[1] = {};
-    uint256 result;
-    CHash256().Write(p1begin == p1end ? pblank : (const unsigned char*)&p1begin[0], (p1end - p1begin) * sizeof(p1begin[0]))
-              .Write(p2begin == p2end ? pblank : (const unsigned char*)&p2begin[0], (p2end - p2begin) * sizeof(p2begin[0]))
-              .Write(p3begin == p3end ? pblank : (const unsigned char*)&p3begin[0], (p3end - p3begin) * sizeof(p3begin[0]))
-              .Finalize((unsigned char*)&result);
-    return result;
-}
-
 /** Compute the 160-bit hash an object. */
 template<typename T1>
 inline uint160 Hash160(const T1 pbegin, const T1 pend)

src/key.h

@@ -56,11 +56,6 @@ public:
         keydata.resize(32);
     }
 
-    //! Destructor (again necessary because of memlocking).
-    ~CKey()
-    {
-    }
-
     friend bool operator==(const CKey& a, const CKey& b)
     {
         return a.fCompressed == b.fCompressed &&

src/uint256.h

@@ -111,7 +111,6 @@ public:
 class uint160 : public base_blob<160> {
 public:
     uint160() {}
-    explicit uint160(const base_blob<160>& b) : base_blob<160>(b) {}
     explicit uint160(const std::vector<unsigned char>& vch) : base_blob<160>(vch) {}
 };
 
@@ -123,7 +122,6 @@ public:
 class uint256 : public base_blob<256> {
 public:
     uint256() {}
-    explicit uint256(const base_blob<256>& b) : base_blob<256>(b) {}
     explicit uint256(const std::vector<unsigned char>& vch) : base_blob<256>(vch) {}
 
     /** A cheap hash function that just returns 64 bits from the result, it can be