Revert "tdf#95687: Wrong function names in Formula Writer are considered as SUM"

This reverts commit 010ed5e6f4505647b0f9043d1cf5001db2057e0d.
The fix was too naive and generated a problem during PythonTest_sw_python with set_expression test
diff --git a/sw/source/core/bastyp/calc.cxx b/sw/source/core/bastyp/calc.cxx
index 52d5eef..1317ec2 100644
--- a/sw/source/core/bastyp/calc.cxx
+++ b/sw/source/core/bastyp/calc.cxx
@@ -713,7 +713,7 @@ SwCalcOper SwCalc::GetToken()
            }
            aVarName = aName;
            eCurrOper = CALC_NAME;
            bSetError = true;
            bSetError = false;
        }
        else if ( aRes.TokenType & KParseType::DOUBLE_QUOTE_STRING )
        {