remove pk and not null constraint from to_ and from_ columns

[jycor]

These columns are not part of the primary key and definitely have null values, so their schema shouldn't say these things are true.

depends on: dolthub/go-mysql-server#3583

[coffeegoddd]

@jycor DOLT

read_tests	from_latency	to_latency	percent_change
covering_index_scan	2.3	2.3	0.0
groupby_scan	142.39	144.97	1.81
index_join	2.0	2.03	1.5
index_join_scan	1.34	1.34	0.0
index_scan	219.36	219.36	0.0
oltp_point_select	0.25	0.25	0.0
oltp_read_only	4.91	5.0	1.83
select_random_points	0.55	0.55	0.0
select_random_ranges	0.64	0.63	-1.56
table_scan	200.47	200.47	0.0
types_table_scan	467.3	458.96	-1.78

write_tests	from_latency	to_latency	percent_change
oltp_delete_insert	6.21	6.21	0.0
oltp_insert	3.13	3.13	0.0
oltp_read_write	11.24	11.24	0.0
oltp_update_index	3.3	3.3	0.0
oltp_update_non_index	3.02	3.02	0.0
oltp_write_only	6.21	6.32	1.77
types_delete_insert	6.91	6.79	-1.74

[coffeegoddd]

@jycor DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
4123092	ok	5937471

version	total_tests
4123092	5937471

correctness_percentage
100.0

[coffeegoddd]

@jycor DOLT

test_name	from_latency_p95	to_latency_p95	percent_change
tpcc-scale-factor-1	45.79	45.79	0.0

test_name	from_server_name	from_server_version	from_tps	to_server_name	to_server_version	to_tps	percent_change
tpcc-scale-factor-1	dolt	2a5de68	52.85	dolt	4310db8	52.53	-0.61

[coffeegoddd]

@jycor DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
9b4baa7	ok	5937471

version	total_tests
9b4baa7	5937471

correctness_percentage
100.0

[zachmu]

LGTM

[coffeegoddd]

@jycor DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
9eaa7d2	ok	5937471

version	total_tests
9eaa7d2	5937471

correctness_percentage
100.0

[coffeegoddd]

@jycor DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
097cf5c	ok	5937471

version	total_tests
097cf5c	5937471

correctness_percentage
100.0

[coffeegoddd]

@jycor DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
4310db8	ok	5937471

version	total_tests
4310db8	5937471

correctness_percentage
100.0