Remove unreachable issues in code (#3793)

remove unreachable links by python scripts:
```
def is_delete_issue(link):
    try:
        response = requests.get(link)
    except RequestException as e:
        print(f"An error occurred while trying to get the link: {e}")
        return False

    return "This issue has been deleted." in response.text


def remove_unreachable_links(dir):
    string_to_search = re.compile(r'// @see https://github\.com/ossrs/srs/issues/.*')
    file_list = util.find_files_with_extension(dir, ".cpp", True)
    for file in file_list:
        lines = []
        with open(file, "r", encoding="utf-8") as f:
            lines = f.readlines()
        with open(file, "w", encoding="utf-8", newline="\n") as f:    
            for line in lines:
                if string_to_search.search(line):
                    result = re.search(r'https://github\.com/ossrs/srs/issues/\d+', line)
                    if result:
                        link = result.group()
                        if is_delete_issue(link):
                            print("is_delete_issue link: file: %s, line: %s" % (file, line))
                            continue
                    
                f.write(line)

if __name__ == "__main__":
    remove_unreachable_links("srs/trunk/src/")
```

trunk/src/app/srs_app_dvr.cpp

@@ -868,7 +868,6 @@ srs_error_t SrsDvrSegmentPlan::update_duration(SrsSharedPtrMessage* msg)
     }
     
     // when wait keyframe, ignore if no frame arrived.
-    // @see https://github.com/ossrs/srs/issues/177
     if (wait_keyframe) {
         if (!msg->is_video()) {
             return err;