content-sqlite: deprecate version 0 checkpoint

Problem: The content-sqlite module currently has backwards
compatibility to "version 0" checkpoints, i.e. just a blobref
without any metadata.  This backwards compatibility was added in

9958fbb

over 3 years ago (2/18/2022).  Future work will re-do how checkpoints
are done in content-sqlite and this backwards compatibility makes some
future work annoying.

Solution: Remove backwards compatibility of "version 0" checkpoints.

Remove related tests in t2010-kvs-snapshot-restore.t and helper
test files.

Author: chu11

src/modules/content-sqlite/content-sqlite.c

@@ -393,22 +393,10 @@ void checkpoint_get_cb (flux_t *h,
     }
     s = (char *)sqlite3_column_text (ctx->checkpt_get_stmt, 0);
     if (!(o = json_loads (s, 0, &error))) {
-        if (blobref_validate (s) < 0) {
-            errstr = error.text;
-            errno = EINVAL;
-            goto error;
-        }
-        /* assume "version 0" if value is a bare blobref and return it
-         * in a json envelope */
-        if (!(o = json_pack ("{s:i s:s s:i s:f}",
-                             "version", 0,
-                             "rootref", s,
-                             "sequence", 0,
-                             "timestamp", 0.))) {
-            errstr = "failed to encode blobref in json envelope";
-            errno = EINVAL;
-            goto error;
-        }
+        /* recovery from version 0 checkpoint blobref not supported */
+        errstr = error.text;
+        errno = EINVAL;
+        goto error;
     }
     if (flux_respond_pack (h,
                            msg,

t/Makefile.am

@@ -410,7 +410,6 @@ dist_check_SCRIPTS = \
 	valgrind/workload.d/resource \
 	content/content-helper.sh \
 	kvs/kvs-helper.sh \
-	kvs/change-checkpoint.py \
 	job-manager/exec-service.lua \
 	job-manager/drain-cancel.py \
 	job-manager/bulk-state.py \

t/kvs/change-checkpoint.py

@@ -9,8 +9,6 @@ test -n "$FLUX_TESTS_LOGFILE" && set -- "$@" --logfile
 
 test_under_flux 1
 
-CHANGECHECKPOINT=${FLUX_SOURCE_DIR}/t/kvs/change-checkpoint.py
-
 #
 # test content-sqlite backing
 #
@@ -78,20 +76,6 @@ test_expect_success 're-run instance, get rootref (sqlite)' '
 		   flux kvs getroot -b > getrootsqlite.out
 '
 
-test_expect_success 'write rootref to checkpoint path, emulating checkpoint version=0 (sqlite)' '
-	rootref=$(cat getrootsqlite.out) &&
-	${CHANGECHECKPOINT} $(pwd)/content.sqlite "kvs-primary" ${rootref}
-'
-
-test_expect_success 're-run instance, verify checkpoint correctly loaded (sqlite)' '
-	flux start --setattr=statedir=$(pwd) \
-		   flux dmesg >dmesgsqlite2.out
-'
-
-test_expect_success 'verify checkpoint loaded with no date (sqlite)' '
-	grep checkpoint dmesgsqlite2.out | grep "N\/A"
-'
-
 #
 # test content-files backing
 #