with open('filenames.txt', 'r', encoding='utf-8') as infile:
    lines  = infile.readlines()
    processed_lines = []
    for line in lines:
        stripped_line = line.rstrip('\n\r')
        if len(stripped_line) > 4:
            new_line = stripped_line[:-4]
        else:
            new_line = ""
        processed_lines.append(new_line + '\n')

    with open('filename_no_extension.txt', 'w', encoding='utf-8') as outfile:
        outfile.writelines(processed_lines)