fix: clean up synth.py for multiple version

[summer-ji-eng]

1. synth.py clean up for multiple version
2. run synthtool update the code

[codecov]

Codecov Report

Merging #396 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #396   +/-   ##
=======================================
  Coverage   98.77%   98.77%           
=======================================
  Files           7        7           
  Lines        9654     9654           
  Branches      375      375           
=======================================
  Hits         9536     9536           
  Misses        114      114           
  Partials        4        4           

Impacted Files	Coverage Δ
src/index.ts	100.00% <100.00%> (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 3edf825...caab0aa. Read the comment docs.

[summer-ji-eng]

DO NOT MERGE until LRO change merge.
TODO:
rebase once LRO PR merged