sculpt: don't install any index by default

When buiding the sculpt image, the sculpt.run script used to integrate
the current version of the index of the 'depot_user' into the boot
image. At runtime, when the Sculpt partition is selected for "use" this
index - along with the 'pubkey' and 'download' files of the known
depot users - is written to the Sculpt partition.

This has the undesirable effect that a later version of the index
(published some time after the sculpt image was created) would always be
overwritten by the outdated index shipped with the boot image.

The built-in default index was actually a stop-gap solution needed
during the development of Sculpt CE, introduced when the downloading of
index files was not yet supported. Now, with the working download
mechanism, it is no longer needed. Hence, this patch removes the default
index from the sculpt image.

repos/gems/run/sculpt.run

@@ -619,8 +619,7 @@ set depot_users_files [exec sh -c "cd [genode_dir]; \
                                    find depot -maxdepth 3 -name pubkey \
                                                       -or -name download"]
 exec sh -c "tar cf [run_dir]/genode/depot_users.tar -C [genode_dir] \
-                   [join $depot_users_files] \
-                   depot/[depot_user]/index/[sculpt_version]"
+                   [join $depot_users_files]"
 
 
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