engine: remove Ubuntu 20.10 "Groovy" (EOL: 2021-07-22)

Signed-off-by: Sebastiaan van Stijn <[email protected]>

Author: thaJeztah

engine/install/ubuntu.md

@@ -28,7 +28,6 @@ To install Docker Engine, you need the 64-bit version of one of these Ubuntu
 versions:
 
 - Ubuntu Hirsute 21.04
-- Ubuntu Groovy 20.10
 - Ubuntu Focal 20.04 (LTS)
 - Ubuntu Bionic 18.04 (LTS)