executor: drop partition information in 'show create table'

[tiancaiamao]

What problem does this PR solve?

Fix show create table in release 2.0

Before this change, create a table like this:

CREATE TABLE t (a int) PARTITION BY RANGE(a) (
 	PARTITION p0 VALUES LESS THAN (10),
 	PARTITION p1 VALUES LESS THAN (20),
 	PARTITION p2 VALUES LESS THAN (MAXVALUE))

show create table results in:

CREATE TABLE t (a int) PARTITION BY RANGE(a) (
 	PARTITION p0 VALUES LESS THAN 10,
 	PARTITION p1 VALUES LESS THAN 20,
 	PARTITION p2 VALUES LESS THAN (MAXVALUE))

It's a illegal SQL and would make syncer broken.

What is changed and how it works?

#6630 fix it in the master branch, but it's hard to cherry-pick.
There is a related fix in show create table like #6332
And also this one #7379
And also some parser related changes for the cherry-pick.

In one word, it's fixed so many times, but never got right.

In this PR, I just drop the partition information, no code, not bug.

Check List

Tests

• Unit test

Side effects

show create table in release 2.0 branch will not display table partition any more.

@shenli @zhexuany @winkyao

[shenli]

Please update the comment in line 592 and remove the following lines.

[tiancaiamao]

PTAL @shenli

[shenli]

LGTM

[tiancaiamao]

PTAL @winkyao @zhexuany

[winkyao]

LGTM

[tiancaiamao]

/run-all-tests

[tiancaiamao]

/run-all-tests tikv=release-2.0 pd=release-2.0 tidb-test=release-2.0

[tiancaiamao]

@shenli

[tiancaiamao]

@shenli Ping