Remove old parser tests

[jakebailey]

These were useful back when we were just porting stuff to verify that we weren't crashing, but now it's 20k extra tests that are largely already tested by the now-working compiler test suite.

[Copilot]

Pull Request Overview

This PR removes the legacy TestParseTypeScriptRepo suite and unused imports to slim down the parser test file.

• Deleted the monolithic TestParseTypeScriptRepo which iterated over the TypeScript submodule.
• Removed now-unused imports (strings, ast) tied to the deleted test.
• Retained and cleaned up the benchmark and parsing helpers.

Comments suppressed due to low confidence (3)

internal/parser/parser_test.go:11

• The repo import is no longer used after removing TestParseTypeScriptRepo; consider deleting this import to avoid dead code.

"github.com/microsoft/typescript-go/internal/repo"

internal/parser/parser_test.go:48

• The parsableFile struct is no longer referenced after removing the parser tests; you may want to remove it to keep the file clean.

type parsableFile struct {

internal/parser/parser_test.go:47

• [nitpick] Removing this broad integration test reduces overall parser coverage; consider adding smaller, targeted unit tests for key syntax scenarios.

func TestParseTypeScriptRepo(t *testing.T) {