[build] Move policy settings to new src/policy/settings unit

This moves the following policy settings functions and globals to a new
src/policy/settings unit in lib_server:

- `incrementalRelayFee`
- `dustRelayFee`
- `nBytesPerSigOp`
- `fIsBareMultisigStd`

These settings are only required by the node and should not be accessed
by other libraries.

src/validation.h

@@ -114,8 +114,6 @@ static const int64_t DEFAULT_MAX_TIP_AGE = 24 * 60 * 60;
 /** Maximum age of our tip in seconds for us to be considered current for fee estimation */
 static const int64_t MAX_FEE_ESTIMATION_TIP_AGE = 3 * 60 * 60;
 
-/** Default for -permitbaremultisig */
-static const bool DEFAULT_PERMIT_BAREMULTISIG = true;
 static const bool DEFAULT_CHECKPOINTS_ENABLED = true;
 static const bool DEFAULT_TXINDEX = false;
 static const unsigned int DEFAULT_BANSCORE_THRESHOLD = 100;
@@ -159,7 +157,6 @@ extern uint256 g_best_block;
 extern std::atomic_bool fImporting;
 extern std::atomic_bool fReindex;
 extern int nScriptCheckThreads;
-extern bool fIsBareMultisigStd;
 extern bool fRequireStandard;
 extern bool fCheckBlockIndex;
 extern bool fCheckpointsEnabled;