Rip out about half the code: levels, enforcement, and STAmount changes

- Changed the EnforceInteger enum into a bool.
- Removed enforcement by throw.
- Essentially got rid of the "weak" and "strong" options.
- Removed integer options from STAmount. Since there's no throwing,
  there's no need to override the default.

include/xrpl/protocol/STNumber.h

@@ -58,11 +58,11 @@ public:
 
     /// Sets the flag on the underlying number
     void
-    setIntegerEnforcement(Number::EnforceInteger enforce);
+    setIsInteger(bool isInteger);
 
     /// Gets the flag value on the underlying number
-    Number::EnforceInteger
-    integerEnforcement() const noexcept;
+    bool
+    isInteger() const noexcept;
 
     /// Checks the underlying number
     bool