[cleanup] Remove unnecessary mirrors, yt-dl's website is updated

README.md

@@ -21,18 +21,13 @@ To install it right away for all UNIX users (Linux, macOS, etc.), type:
 
     sudo curl -L https://yt-dl.org/downloads/latest/youtube-dl -o /usr/local/bin/youtube-dl
     sudo chmod a+rx /usr/local/bin/youtube-dl
-    
-Mirror:
-    
-    sudo curl -L https://dl.netsyms.net/programs/youtube-dl/latest/youtube-dl -o /usr/local/bin/youtube-dl
-    sudo chmod a+rx /usr/local/bin/youtube-dl
 
 If you do not have curl, you can alternatively use a recent wget:
 
     sudo wget https://yt-dl.org/downloads/latest/youtube-dl -O /usr/local/bin/youtube-dl
     sudo chmod a+rx /usr/local/bin/youtube-dl
 
-Windows users can [download an .exe file](https://yt-dl.org/latest/youtube-dl.exe) ([mirror](https://dl.netsyms.net/programs/youtube-dl/latest/youtube-dl.exe)) and place it in any location on their [PATH](https://en.wikipedia.org/wiki/PATH_%28variable%29) except for `%SYSTEMROOT%\System32` (e.g. **do not** put in `C:\Windows\System32`).
+Windows users can [download an .exe file](https://yt-dl.org/latest/youtube-dl.exe) and place it in any location on their [PATH](https://en.wikipedia.org/wiki/PATH_%28variable%29) except for `%SYSTEMROOT%\System32` (e.g. **do not** put in `C:\Windows\System32`).
 
 You can also use pip: