Revert merge of pull #4845

It breaks the new mingw tests!

See

- https://travis-ci.org/bitcoin/bitcoin/jobs/36845581
- https://travis-ci.org/bitcoin/bitcoin/jobs/36845582

This reverts commit 4705902777, 5e2e7fcb99, a25fd6be13.

src/chainparams.h

@@ -61,8 +61,6 @@ public:
     bool DefaultCheckMemPool() const { return fDefaultCheckMemPool; }
     /* Allow mining of a min-difficulty block */
     bool AllowMinDifficultyBlocks() const { return fAllowMinDifficultyBlocks; }
-    /* Skip proof-of-work check: allow mining of any difficulty block */
-    bool SkipProofOfWorkCheck() const { return fSkipProofOfWorkCheck; }
     /* Make standard checks */
     bool RequireStandard() const { return fRequireStandard; }
     int64_t TargetTimespan() const { return nTargetTimespan; }
@@ -105,27 +103,8 @@ protected:
     bool fAllowMinDifficultyBlocks;
     bool fRequireStandard;
     bool fMineBlocksOnDemand;
-    bool fSkipProofOfWorkCheck;
 };
 
-/** Modifiable parameters interface is used by test cases to adapt the parameters in order
-*** to test specific features more easily. Test cases should always restore the previous
-*** values after finalization.
-**/
-
-class CModifiableParams {
-public:
-    // Published setters to allow changing values in unit test cases
-    virtual void setSubsidyHalvingInterval(int anSubsidyHalvingInterval) =0;
-    virtual void setEnforceBlockUpgradeMajority(int anEnforceBlockUpgradeMajority)=0;
-    virtual void setRejectBlockOutdatedMajority(int anRejectBlockOutdatedMajority)=0;
-    virtual void setToCheckBlockUpgradeMajority(int anToCheckBlockUpgradeMajority)=0;
-    virtual void setDefaultCheckMemPool(bool aDefaultCheckMemPool)=0;
-    virtual void setAllowMinDifficultyBlocks(bool aAllowMinDifficultyBlocks)=0;
-    virtual void setSkipProofOfWorkCheck(bool aSkipProofOfWorkCheck)=0;
-};
-
-
 /**
  * Return the currently selected parameters. This won't change after app startup
  * outside of the unit tests.
@@ -135,9 +114,6 @@ const CChainParams &Params();
 /** Return parameters for the given network. */
 CChainParams &Params(CBaseChainParams::Network network);
 
-/** Get modifyable network parameters (UNITTEST only) */
-CModifiableParams *ModifiableParams();
-
 /** Sets the params returned by Params() to those for the given network. */
 void SelectParams(CBaseChainParams::Network network);