Remove debug-only assert method (#74996)

This method is only used in one place, only wraps one method call, and can cause people to accidentally select the wrong method in RELEASE mode. I've just inlined the content and removed the method.

src/Compilers/CSharp/Portable/Binder/Semantics/OverloadResolution/OverloadResolution.cs

@@ -3126,17 +3126,6 @@ public override BoundNode VisitReturnStatement(BoundReturnStatement node)
 
         private const int BetterConversionTargetRecursionLimit = 100;
 
-#if DEBUG
-        private BetterResult BetterConversionTarget(
-            TypeSymbol type1,
-            TypeSymbol type2,
-            ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
-        {
-            bool okToDowngradeToNeither;
-            return BetterConversionTargetCore(null, type1, default(Conversion), type2, default(Conversion), ref useSiteInfo, out okToDowngradeToNeither, BetterConversionTargetRecursionLimit);
-        }
-#endif
-
         private BetterResult BetterConversionTargetCore(
             TypeSymbol type1,
             TypeSymbol type2,
@@ -3415,7 +3404,7 @@ private bool CanDowngradeConversionFromLambdaToNeither(BetterResult currentResul
                             Debug.Assert(
                                 r1.IsErrorType() ||
                                 r2.IsErrorType() ||
-                                currentResult == BetterConversionTarget(r1, r2, ref useSiteInfo));
+                                currentResult == BetterConversionTargetCore(null, type1, default(Conversion), type2, default(Conversion), ref useSiteInfo, out _, BetterConversionTargetRecursionLimit));
                         }
 #endif
                     }