fix(schema): remove abstract field

- Search engines do not consume the abstract property
- Platforms (Docusaurus, Vitepress, WordPress, Medium) do not use it
- .Summary method does not match the definition of abstract in schema.org

layouts/partials/schema.html

@@ -25,7 +25,6 @@
     "name": "{{ .Title | safeJS }}",
     "headline": "{{ .Title | safeJS }}",
     {{ with .Description }}"description": "{{ . | safeJS }}",{{ end }}
-    {{ with .Summary }}"abstract": "{{ . | safeJS }}",{{ end }}
     {{ with .Site.LanguageCode }}"inLanguage": "{{ . }}",{{ end }}
     "url" : {{ .Permalink }},
     "author" : {