Remove unused classes and stray headers

Found by reviewing headers with 1 or less matching includes:
```
find -name thirdparty -prune -o -name "*.h" -exec basename {} \; | sort -u > headers
for header in $(cat headers); do echo "$header: "; rg -l "#include \"(.*/)?$header\"" | wc -l; done > list-includes
```

servers/visual/rasterizer_rd/shader_rd.cpp

@@ -29,6 +29,7 @@
 /*************************************************************************/
 
 #include "shader_rd.h"
+
 #include "core/string_builder.h"
 #include "rasterizer_rd.h"
 #include "servers/visual/rendering_device.h"