remove unnecessary usage of deprecated BackstageTheme

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

.changeset/six-books-arrive.md

@@ -0,0 +1,23 @@
+---
+'@backstage/plugin-techdocs-module-addons-contrib': patch
+'@backstage/plugin-microsoft-calendar': patch
+'@backstage/plugin-scaffolder-react': patch
+'@backstage/plugin-catalog-graph': patch
+'@backstage/plugin-cost-insights': patch
+'@backstage/plugin-tech-insights': patch
+'@backstage/plugin-code-climate': patch
+'@backstage/plugin-scaffolder': patch
+'@backstage/plugin-gcalendar': patch
+'@backstage/plugin-org-react': patch
+'@backstage/plugin-sonarqube': patch
+'@backstage/plugin-xcmetrics': patch
+'@backstage/plugin-api-docs': patch
+'@backstage/plugin-playlist': patch
+'@backstage/plugin-catalog': patch
+'@backstage/plugin-explore': patch
+'@backstage/plugin-bazaar': patch
+'@backstage/plugin-search': patch
+'@backstage/plugin-org': patch
+---
+
+Internal theme type updates