cleanup: remove .gds.br support

We now use .oas instead

requirements.txt

@@ -1,11 +1,9 @@
 #
-# This file is autogenerated by pip-compile with Python 3.10
+# This file is autogenerated by pip-compile with Python 3.12
 # by the following command:
 #
 #    pip-compile
 #
-brotli==1.1.0
-    # via tt-support-tools (pyproject.toml)
 cairocffi==1.7.1
     # via cairosvg
 cairosvg==2.8.2
@@ -30,8 +28,6 @@ defusedxml==0.7.1
     # via cairosvg
 distlib==0.4.0
     # via virtualenv
-exceptiongroup==1.3.0
-    # via pytest
 filelock==3.18.0
     # via virtualenv
 find-libpython==0.4.1
@@ -93,13 +89,6 @@ tinycss2==1.4.0
     # via
     #   cairosvg
     #   cssselect2
-tomli==2.2.1
-    # via pytest
-typing-extensions==4.15.0
-    # via
-    #   exceptiongroup
-    #   gdstk
-    #   mistune
 urllib3==2.5.0
     # via requests
 virtualenv==20.33.1