Revert "Implement Decimal.Truncate"

This reverts commit 63a5b2a.

Author: hazzik

src/NHibernate.Test/NHSpecificTest/GH0831/FixtureByCode.cs

@@ -135,18 +135,6 @@ public void CanHandleFloor()
 				CanSelect(e => decimal.Floor(e.EntityValue));
 			});
 		}
-	
-		[Test]
-		public void CanHandleTruncate()
-		{
-			AssumeFunctionSupported("truncate");
-
-			Assert.Multiple(() =>
-			{
-				CanFilter(e => decimal.Truncate(e.EntityValue) > 1.0m);
-				CanSelect(e => decimal.Truncate(e.EntityValue));
-			});
-		}
 
 		[Test]
 		public void CanHandleMultiply()

src/NHibernate/Linq/Functions/MathGenerator.cs

@@ -55,7 +55,6 @@ public MathGenerator()
 
 				ReflectHelper.GetMethodDefinition(() => Math.Truncate(default(decimal))),
 				ReflectHelper.GetMethodDefinition(() => Math.Truncate(default(double))),
-				ReflectHelper.GetMethodDefinition(() => decimal.Truncate(default(decimal))),
 
 				ReflectHelper.GetMethodDefinition(() => Math.Pow(default(double), default(double))),
 			};