refactor: remove some usages of default in template

No longer needed thanks to Hugo's configuration merge

layouts/partials/head/colorScheme.html

@@ -1,5 +1,5 @@
-{{- $defaultColorScheme := default "auto" .Site.Params.colorScheme.default -}}
-{{- if not (default false .Site.Params.colorScheme.toggle) -}}
+{{- $defaultColorScheme := .Site.Params.colorScheme.default -}}
+{{- if not .Site.Params.colorScheme.toggle -}}
     {{/* If toggle is disabled, force default scheme */}}
     <script>
         (function() {

layouts/partials/head/opengraph/provider/twitter.html

@@ -11,6 +11,6 @@
 
 {{- $image := partialCached "helper/image" (dict "Context" . "Type" "opengraph") .RelPermalink "opengraph" -}}
 {{- if $image.exists -}}
-    <meta name="twitter:card" content="{{ default `summary_large_image` .Site.Params.opengraph.twitter.card }}">
+    <meta name="twitter:card" content="{{ .Site.Params.opengraph.twitter.card }}">
     <meta name="twitter:image" content='{{ absURL $image.permalink }}' />
 {{- end -}}