go/store/nbs: store.go: Change memtable reference sanity check to happen at table_set.append() instead of trying to check novel chunk sources.

[reltuk]

Removes enforce completeness functionality from ValueStore, which becomes superfluous.

[andy-wm-arthur]

LGTM

[andy-wm-arthur]

should we clear the memtable in errorIfDangling? is there ever a path where we don't want to clear it?

[github-actions]

@coffeegoddd DOLT

test_name	detail	row_cnt	sorted	mysql_time	sql_mult	cli_mult
batching	LOAD DATA	10000	1	0.05	1
batching	batch sql	10000	1	0.09	1.67
batching	by line sql	10000	1	0.08	1.88
blob	1 blob	200000	1	1.02	3.61	3.82
blob	2 blobs	200000	1	1.01	4.83	5.09
blob	no blob	200000	1	1.02	1.56	1.75
col type	datetime	200000	1	0.97	1.97	2.14
col type	varchar	200000	1	0.75	2.52	2.65
config width	2 cols	200000	1	0.82	1.77	1.82
config width	32 cols	200000	1	2.08	1.72	2.54
config width	8 cols	200000	1	1.05	1.72	2.23
pk type	float	200000	1	0.98	1.43	1.56
pk type	int	200000	1	0.86	1.59	1.71
pk type	varchar	200000	1	1.79	1.83	1.94
row count	1.6mm	1600000	1	6.4	1.83	1.96
row count	400k	400000	1	1.62	1.78	1.88
row count	800k	800000	1	3.25	1.78	1.9
secondary index	four index	200000	1	4.59	1.41	1.47
secondary index	no secondary	200000	1	1.02	1.57	1.75
secondary index	one index	200000	1	1.31	1.73	1.89
secondary index	two index	200000	1	2.49	1.47	1.56
sorting	shuffled 1mm	1000000	0	6.64	1.88	1.92
sorting	sorted 1mm	1000000	1	6.39	1.94	2.02

[github-actions]

@coffeegoddd DOLT

name	mean	mean_mult
dolt_blame_basic	37.77	1.38
dolt_blame_commit_filter	205.03	2.79
dolt_commit_ancestors_commit_filter	0.45	1.15
dolt_commits_commit_filter	0.39	0.98
dolt_diff_log_join_from_commit	112.75	1.34
dolt_diff_log_join_to_commit	111.77	1.32
dolt_diff_table_from_commit_filter	0.73	1.18
dolt_diff_table_to_commit_filter	0.71	1.18
dolt_diffs_commit_filter	0.45	1.07
dolt_history_commit_filter	0.69	1.23
dolt_log_commit_filter	0.38	0.95