[MOVEONLY] consensus: move amount.h into consensus

Move amount.h to consensus/amount.h.
Renames, adds missing and removes uneeded includes.

src/test/fuzz/script_flags.cpp

@@ -2,6 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <consensus/amount.h>
 #include <pubkey.h>
 #include <script/interpreter.h>
 #include <streams.h>