chore(cleanup): delete dead test helpers result-assertions + output-assertions

Both modules were defined as test-utility libraries but zero tests
adopted them — 13 + 12 = 25 unused exports across 433 + 499 = 932 LOC.
Drops both files and the matching `export * from` lines in
helpers/index.mts.

Author: jdalton

packages/cli/test/helpers/index.mts

@@ -11,7 +11,5 @@ export * from './generate-report-test-helpers.mts'
 export * from './handle-test-helpers.mts'
 export * from './mock-setup.mts'
 export * from './mocks.mts'
-export * from './output-assertions.mts'
-export * from './result-assertions.mts'
 export * from './test-fixtures.mts'
 export * from './workspace-helper.mts'