Update method 'RemoveDummyFunction' to handle an unexpected DummyFunction suffix. Previously we sometimes failed to remove some forms of DummyFunctions.

EPPlus/ExcelWorksheet.cs

diff --git a/EPPlus/ExcelWorksheet.cs b/EPPlus/ExcelWorksheet.cs
index 982c081..81f5696 100644
--- a/EPPlus/ExcelWorksheet.cs
+++ b/EPPlus/ExcelWorksheet.cs
@@ -124,7 +124,7 @@
             {
                 const string DummyFunctionConcatenate = "\"&\"";
                 const string DummyFunctionPrefix = "IFERROR(__xludf.DUMMYFUNCTION(\"";
-                const string DummyFunctionSuffix = "\"),\"";
+                const string DummyFunctionSuffix = "\"),";
 
                 if (string.IsNullOrEmpty(formula))
                     return formula;