refactor: Retire fixUniversalNumber amendment

Remove all conditional code paths guarded by fixUniversalNumber, keeping
only the "enabled" path since the amendment is now permanently active.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

include/xrpl/protocol/AMMCore.h

@@ -65,7 +65,7 @@ invalidAMMAssetPair(
 std::optional<std::uint8_t>
 ammAuctionTimeSlot(std::uint64_t current, STObject const& auctionSlot);
 
-/** Return true if required AMM amendments are enabled
+/** Return true if required AMM amendment is enabled
  */
 bool
 ammEnabled(Rules const&);

include/xrpl/protocol/IOUAmount.h

@@ -1,6 +1,5 @@
 #pragma once
 
-#include <xrpl/basics/LocalValue.h>
 #include <xrpl/basics/Number.h>
 #include <xrpl/beast/utility/Zero.h>
 
@@ -179,36 +178,4 @@ to_string(IOUAmount const& amount);
 IOUAmount
 mulRatio(IOUAmount const& amt, std::uint32_t num, std::uint32_t den, bool roundUp);
 
-// Since many uses of the number class do not have access to a ledger,
-// getSTNumberSwitchover needs to be globally accessible.
-
-bool
-getSTNumberSwitchover();
-
-void
-setSTNumberSwitchover(bool v);
-
-/** RAII class to set and restore the Number switchover.
- */
-
-class NumberSO
-{
-    bool saved_;
-
-public:
-    ~NumberSO()
-    {
-        setSTNumberSwitchover(saved_);
-    }
-
-    NumberSO(NumberSO const&) = delete;
-    NumberSO&
-    operator=(NumberSO const&) = delete;
-
-    explicit NumberSO(bool v) : saved_(getSTNumberSwitchover())
-    {
-        setSTNumberSwitchover(v);
-    }
-};
-
 }  // namespace xrpl