Consensus: Policy: MOVEONLY: Move CFeeRate out of the consensus module

...from amount.o to policy/feerate.o

Policy, because it moves policy code to the policy directory (common module)

src/validation.h

@@ -14,6 +14,7 @@
 #include "coins.h"
 #include "fs.h"
 #include "protocol.h" // For CMessageHeader::MessageStartChars
+#include "policy/feerate.h"
 #include "script/script_error.h"
 #include "sync.h"
 #include "versionbits.h"