[C][Client][Clang Static Analyzer] Remove the useless free operation for buffContent

[ityuhui]

This is a defect introduced by my PR #7285

            list_ForEach(listEntry, contentType) {
                if(strstr((char *) listEntry->data,
                          "xml") == NULL)
                {
                    buffContent =
                        malloc(strlen(
                                   "Content-Type: ") + strlen(
                                   (char *)
                                   listEntry->data) +
                               1);
                    ...
                    free(buffContent);  // <-- I add code to free "buffContent" in PR 7285
                    buffContent = NULL;
                }
...

        if(contentType != NULL) {.   // <-- but I forgot to remove this code, so it will coredump here because buffContent is freed before.	
            free(buffContent);	
        }

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@wing328 @zhemant @michelealbano

[wing328]

@ityuhui thanks for the quick fix.