fix(lambda-at-edge): handle prerender-manifest v3 locales properly

[dphang]

Fixes: #907

• Recent Next.js version has a key for each locale in the prerender manifest routes, so we don't need to build it manually anymore. Only if version <= 2 will it do so.

[codecov]

Codecov Report

Merging #910 (bbf21c4) into master (83c8c6d) will decrease coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #910      +/-   ##
==========================================
- Coverage   81.31%   81.28%   -0.03%     
==========================================
  Files          68       68              
  Lines        2488     2490       +2     
  Branches      591      592       +1     
==========================================
+ Hits         2023     2024       +1     
- Misses        398      399       +1     
  Partials       67       67              

Impacted Files	Coverage Δ
packages/libs/lambda-at-edge/src/build.ts	89.93% <66.66%> (-0.25%)	⬇️

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