Remove gdsii module index

It is not useful and just add one more level of TOC.

Author: eugmes

doc/gdsii/index.rst

@@ -14,7 +14,13 @@ Contents:
 .. toctree::
    :maxdepth: 2
 
-   gdsii/index
+   gdsii/library
+   gdsii/structure
+   gdsii/elements
+   gdsii/tags
+   gdsii/types
+   gdsii/record
+   gdsii/exceptions
 
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