Remove redundant explicitly defined copy ctors

CFeeRate and CTxMemPoolEntry have explicitly defined copy ctors which has the same functionality as the implicit default copy ctors which would have been generated otherwise.

Besides being redundant, it violates the rule of three (see https://en.wikipedia.org/wiki/Rule_of_three_(C%2B%2B_programming) ).
(Of course, the rule of three doesn't -really- cause a resource management issue here, but the reason for that is exactly that there is no need for an explicit copy ctor in the first place since no resources are being managed).
CFeeRate has an explicitly defined copy ctor which has the same functionality as the implicit default copy ctor which would h
ave been generated otherwise.

src/policy/feerate.h

@@ -26,7 +26,6 @@ public:
     explicit CFeeRate(const CAmount& _nSatoshisPerK): nSatoshisPerK(_nSatoshisPerK) { }
     /** Constructor for a fee rate in satoshis per kB. The size in bytes must not exceed (2^63 - 1)*/
     CFeeRate(const CAmount& nFeePaid, size_t nBytes);
-    CFeeRate(const CFeeRate& other) { nSatoshisPerK = other.nSatoshisPerK; }
     /**
      * Return the fee in satoshis for the given size in bytes.
      */

src/txmempool.cpp

@@ -39,11 +39,6 @@ CTxMemPoolEntry::CTxMemPoolEntry(const CTransactionRef& _tx, const CAmount& _nFe
     nSigOpCostWithAncestors = sigOpCost;
 }
 
-CTxMemPoolEntry::CTxMemPoolEntry(const CTxMemPoolEntry& other)
-{
-    *this = other;
-}
-
 void CTxMemPoolEntry::UpdateFeeDelta(int64_t newFeeDelta)
 {
     nModFeesWithDescendants += newFeeDelta - feeDelta;

src/txmempool.h

@@ -95,8 +95,6 @@ public:
                     bool spendsCoinbase,
                     int64_t nSigOpsCost, LockPoints lp);
 
-    CTxMemPoolEntry(const CTxMemPoolEntry& other);
-
     const CTransaction& GetTx() const { return *this->tx; }
     CTransactionRef GetSharedTx() const { return this->tx; }
     const CAmount& GetFee() const { return nFee; }