Remove "default_tags" as it's too similar to "default_tag" (#38)

Reviewed-on: https://codeberg.org/woodpecker-plugins/plugin-docker-buildx/pulls/38
Reviewed-by: Lauris BH <lafriks@noreply.codeberg.org>
Co-authored-by: 6543 <6543@obermui.de>
Co-committed-by: 6543 <6543@obermui.de>

cmd/docker-buildx/config.go

@@ -123,7 +123,7 @@ func settingsFlags(settings *plugin.Settings) []cli.Flag {
 		},
 		&cli.BoolFlag{
 			Name:        "tags.auto",
-			EnvVars:     []string{"PLUGIN_DEFAULT_TAGS", "PLUGIN_AUTO_TAG"},
+			EnvVars:     []string{"PLUGIN_AUTO_TAG"},
 			Usage:       "generates tag names automatically based on git branch and git tag",
 			Destination: &settings.Build.TagsAuto,
 		},