configure.py: Fix unified-package version and release to unbreak "dist" target
configure.py: Fix unified-package version and release to unbreak "dist" target

The "dist" target fails as follows:

  $ ./tools/toolchain/dbuild ninja dist
  ninja: error: 'build/dev/scylla-unified-package-..tar.gz', needed by 'dist-unified-tar', missing and no known rule to make it

Fix two issues:

- Fix Python variable references to "scylla_version" and
  "scylla_release", broken by commit bec0c15ee9 ("configure.py: Add
  version to unified tarball filename"). The breakage went unnoticed
  because ninja default target does not call into dist...

- Remove dependencies to build/<mode>/scylla-unified-package.tar.gz. The
  file is now in build/<mode>/dist/tar/ directory and contains version
  and release in the filename.

Message-Id: <fa16701ac80daabf7427f9a5cbe65bd03a7faf53@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla