Remove last_modified plugin config

This no longer needed, because the pages have been changed to use the
site upload date, instead.

.github/workflows/docs.yaml

@@ -33,7 +33,7 @@ jobs:
         run: sudo apt-get install -y ruby-full build-essential zlib1g-dev
 
       - name: Install required Ruby gems
-        run: sudo gem install bundler jekyll jekyll-theme-cayman jekyll-last-modified-at
+        run: sudo gem install bundler jekyll jekyll-theme-cayman
 
       - name: Build the schema browser site
         run: jekyll build

Makefile

@@ -16,8 +16,7 @@ init:
 		echo >&2 "For more information, visit: https://jekyllrb.com/docs/installation"; \
 		exit 1; \
 	}
-	gem install -q --silent --no-verbose jekyll bundler jekyll-theme-cayman jekyll-last-modified-at
-
+	gem install -q --silent --no-verbose jekyll bundler jekyll-theme-cayman
 # Run the web server and watch for changes
 run:
 	jekyll serve --watch

_config.yml

@@ -1,8 +1,4 @@
 theme: jekyll-theme-cayman
-plugins:
-  - jekyll-last-modified-at
-last-modified-at:
-  date-format: '%B %d, %Y'
 
 data_dir: ./yml
 layouts_dir: _layouts