refactor: cleanup query generators

[sushantdhiman]

Pull Request check-list

Please make sure to review and check all of these items:

• Does npm run test or npm run test-DIALECT pass with this change (including linting)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
• Have you added new tests to prevent regressions?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Did you update the typescript typings accordingly (if applicable)?
• Did you follow the commit message conventions explained in CONTRIBUTING.md?

Description of change

Rename / remove some internal methods

[codecov]

Codecov Report

Merging #12304 into master will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #12304      +/-   ##
==========================================
+ Coverage   96.29%   96.40%   +0.10%     
==========================================
  Files          95       95              
  Lines        9127     9117      -10     
==========================================
  Hits         8789     8789              
+ Misses        338      328      -10     

Impacted Files	Coverage Δ
lib/dialects/mssql/query-generator.js	95.69% <ø> (ø)
lib/dialects/mysql/query-generator.js	97.56% <ø> (ø)
lib/dialects/postgres/query-generator.js	94.93% <100.00%> (+2.46%)	⬆️

---

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 4d9165b...d848891. Read the comment docs.