Remove dead code: debug blocks, unused variable, stale fprintf

[timsehn]

Summary

• Remove #if 0 debug fprintf block in prolly_mutate.c mergeWalk
• Remove debug fprintf on GC chunk read failure in doltlite_gc.c
• Remove unused found variable in doltlite.c dolt_add

Test plan

• 107/107 parity tests pass

🤖 Generated with Claude Code

[github-actions]

Sysbench-Style Benchmark: Doltlite vs SQLite

In-Memory

Reads

Test	SQLite (ms)	Doltlite (ms)	Multiplier
oltp_point_select	55	56	1.02
oltp_range_select	31	36	1.16
oltp_sum_range	13	16	1.23
oltp_order_range	5	5	1.00
oltp_distinct_range	7	7	1.00
oltp_index_scan	6	110	18.33
select_random_points	24	64	2.67
select_random_ranges	8	8	1.00
covering_index_scan	14	118	8.43
groupby_scan	50	57	1.14
index_join	5	8	1.60
index_join_scan	2	485	242.50
types_table_scan	10	13	1.30
table_scan	2	2	1.00
oltp_read_only	225	257	1.14

Writes

Test	SQLite (ms)	Doltlite (ms)	Multiplier
oltp_bulk_insert	27	36	1.33
oltp_insert	24	27	1.12
oltp_update_index	46	12379	269.11
oltp_update_non_index	35	45	1.29
oltp_delete_insert	44	47517	1079.93
oltp_write_only	18	4963	275.72
types_delete_insert	31	31	1.00
oltp_read_write	123	5024	40.85

File-Backed

Reads

Test	SQLite (ms)	Doltlite (ms)	Multiplier
oltp_point_select	209	78	0.37
oltp_range_select	49	39	0.80
oltp_sum_range	24	18	0.75
oltp_order_range	6	6	1.00
oltp_distinct_range	9	8	0.89
oltp_index_scan	17	104	6.12
select_random_points	35	67	1.91
select_random_ranges	20	24	1.20
covering_index_scan	22	133	6.05
groupby_scan	54	63	1.17
index_join	12	10	0.83
index_join_scan	4	479	119.75
types_table_scan	12	14	1.17
table_scan	2	1	0.50
oltp_read_only	388	273	0.70

Writes

Test	SQLite (ms)	Doltlite (ms)	Multiplier
oltp_bulk_insert	31	43	1.39
oltp_insert	23	39	1.70
oltp_update_index	49	12368	252.41
oltp_update_non_index	37	51	1.38
oltp_delete_insert	47	50344	1071.15
oltp_write_only	23	5455	237.17
types_delete_insert	27	31	1.15
oltp_read_write	131	5462	41.69

10000 rows, single CLI invocation per test, workload-only timing via SQL timestamps.