gnu: qtsvg: Rename variable to qtsvg-5.

This is in preparation of the qtsvg update to version 6.

This change was automated via the following command:

  git grep -l '\bqtsvg\b' | xargs sed 's/qtsvg/qtsvg-5/g' -i

gnu/packages/robotics.scm

@@ -118,7 +118,7 @@ hundred times faster than real-time.")
              enki
              protobuf-3.5 ;for logging
              qtbase-5
-             qtsvg
+             qtsvg-5
              qttools ;for libQt5Help, needed by "studio"
              qtwebkit
              qtx11extras