chore: remove unused rollup-plugin-typescript ambient module types

[dnalborczyk]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

missed this during the @rollup/plugin-typescript bump.

also fixed the return type of is_reference.

[codecov]

Codecov Report

Merging #4233 (6a9e41e) into master (b67ef30) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4233   +/-   ##
=======================================
  Coverage   98.39%   98.39%           
=======================================
  Files         203      203           
  Lines        7341     7341           
  Branches     2087     2087           
=======================================
  Hits         7223     7223           
  Misses         58       58           
  Partials       60       60           

Impacted Files	Coverage Δ
src/ast/nodes/Identifier.ts	100.00% <100.00%> (ø)

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