feat: remove builtin constants

[tserg]

What I did

Builtin constants like MAX_INT128, MIN_INT128, MIN_DECIMAL, MAX_DECIMAL and MAX_UINT256 have been deprecated since v0.3.4 with the introduction of the min_value and max_value builtins, and further back for ZERO_ADDRESS and EMPTY_BYTES32 with the empty builtin.

This PR removes them from the language entirely, and will be a breaking change.

How I did it

Delete code.

How to verify it

See tests.

Commit message

feat: remove builtin constants

the current set of builtin constants are no longer needed since the 
introduction of `min_value`, `max_value` and `empty` builtins.

Description for the changelog

Remove builtin constants.

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #3350 (caffd02) into master (68da04b) will increase coverage by 0.34%.
The diff coverage is n/a.

❗ Current head caffd02 differs from pull request most recent head 2483099. Consider uploading reports for the commit 2483099 to get more accurate results

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@@            Coverage Diff             @@
##           master    #3350      +/-   ##
==========================================
+ Coverage   88.66%   89.01%   +0.34%     
==========================================
  Files          86       86              
  Lines       11467    11440      -27     
  Branches     2607     2605       -2     
==========================================
+ Hits        10167    10183      +16     
+ Misses        873      835      -38     
+ Partials      427      422       -5     

Files	Coverage Δ
vyper/ast/folding.py	92.72% <ø> (-0.56%)	⬇️
vyper/compiler/phases.py	93.02% <ø> (+0.65%)	⬆️

... and 17 files with indirect coverage changes

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[charles-cooper]

i'm pretty ok with merging this even for the 0.3.x series tbh. the old constants have been emitting warnings for nearly a year. @fubuloubu thoughts?

[fubuloubu]

Sure, I think that seems realtively low-impact, but definitely worth broadcasting the breaking change

[charles-cooper]

nice cleanup!