Remove fluter tool usage of protobuf

[jonahwilliams]

Description

It looks protobuf is going to have some upcoming breaking changes. I don't want to deal with these, so instead I'll just switch back to JSON.

[codecov]

Codecov Report

Merging #40410 into master will increase coverage by 0.01%.
The diff coverage is 87.09%.

@@            Coverage Diff             @@
##           master   #40410      +/-   ##
==========================================
+ Coverage   59.59%    59.6%   +0.01%     
==========================================
  Files         192      191       -1     
  Lines       18602    18572      -30     
==========================================
- Hits        11086    11070      -16     
+ Misses       7516     7502      -14

Flag	Coverage Δ
#flutter_tool	59.6% <87.09%> (+0.01%)	⬆️

Impacted Files	Coverage Δ
...lutter_tools/lib/src/commands/update_packages.dart	3.63% <ø> (ø)	⬆️
...er_tools/lib/src/build_system/file_hash_store.dart	90.32% <87.09%> (-2.37%)	⬇️
packages/flutter_tools/lib/src/version.dart	90.99% <0%> (-1.9%)	⬇️
packages/flutter_tools/lib/src/cache.dart	43.5% <0%> (-0.73%)	⬇️
packages/flutter_tools/lib/src/commands/run.dart	64.03% <0%> (+0.49%)	⬆️

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[zanderso]

lgtm w/ question

[zanderso]

Does this also need to be removed from the BUILD.gn?

[jonahwilliams]

We technically still depend on this transitively...I'm not sure. I'd rather leave it in to be safe