svgo: remove deprecated --enable=plugin_name example (#6379)

The `--enable` flag was removed in SVGO 2.0. For now, the only way to enable optional plugins is via config. Setting up a config file is out of scope for tldr so I'm just removing the deprecated flag in this PR.

See: https://github.com/svg/svgo/releases/tag/v2.0.0

pages/common/svgo.md

@@ -28,10 +28,6 @@
 
 `svgo {{test.svg}} -o -`
 
-- Optimize a file making sure a given plugin is enabled:
-
-`svgo --enable={{plugin_name}}`
-
 - Show available plugins:
 
 `svgo --show-plugins`