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/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