refactor: Replace !=/== tesSuccess with using isTesSuccess (#6409)

This change replaces all instances of `<variable> != tesSUCCESS` with `!isTesSuccess(<variable>)` and `<variable> == tesSUCCESS` with `isTesSuccess(<variable>)`.

src/test/app/AMM_test.cpp

@@ -3089,7 +3089,7 @@ private:
                 PreflightContext pfCtx(
                     env.app(), *jtx.stx, env.current()->rules(), tapNONE, env.journal);
                 auto pf = Transactor::invokePreflight<AMMBid>(pfCtx);
-                BEAST_EXPECT(pf != tesSUCCESS);
+                BEAST_EXPECT(!isTesSuccess(pf));
             }
 
             {