fix(query): revise the length of var data type.

source/libs/scalar/src/sclfunc.c

@@ -709,10 +709,6 @@ int32_t castFunction(SScalarParam *pInput, int32_t inputNum, SScalarParam *pOutp
   int16_t outputType = GET_PARAM_TYPE(&pOutput[0]);
   int64_t outputLen  = GET_PARAM_BYTES(&pOutput[0]);
 
-  if (IS_VAR_DATA_TYPE(outputType)) {
-    outputLen += VARSTR_HEADER_SIZE;
-  }
-
   char *outputBuf = taosMemoryCalloc(outputLen * pInput[0].numOfRows, 1);
   char *output = outputBuf;