remove expired coolapk download url (#116)

Author: nchj

shizuku/download.md

@@ -4,6 +4,4 @@
 
 [GitHub Release](https://github.com/RikkaApps/Shizuku/releases)
 
-[Coolapk](https://www.coolapk.com/apk/moe.shizuku.privileged.api)
-
-[IzzyOnDroid F-Droid Repository](https://apt.izzysoft.de/fdroid/index/apk/moe.shizuku.privileged.api)
+[IzzyOnDroid F-Droid Repository](https://apt.izzysoft.de/fdroid/index/apk/moe.shizuku.privileged.api)