clean up error code and message for parser

[lysu]

What problem does this PR solve?

following pingcap/tidb#12866 in the parser

What is changed and how it works?

clean up error code and message for the parser in yy_parser.go

remove unnecessary const code define

Check List

Tests

• Unit test
• Integration test

Code changes

• remove code

Side effects

• n/a

Related changes

• Need to cherry-pick to the release branch

---

This change is 

[zz-jason]

LGTM

[codecov]

Codecov Report

Merging #618 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #618   +/-   ##
=======================================
  Coverage   79.77%   79.77%           
=======================================
  Files          32       32           
  Lines       12578    12578           
=======================================
  Hits        10034    10034           
  Misses       1948     1948           
  Partials      596      596

Impacted Files	Coverage Δ
charset/charset.go	87.01% <ø> (ø)	⬆️
types/etc.go	89.47% <ø> (ø)	⬆️
yy_parser.go	83.46% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update afbd9b8...89761bd. Read the comment docs.

[tangenta]

LGTM