feat(core)!: Remove flatten method (#14784)

ref: #14268

Deprecation PR:
#14454

Removes `flatten`. This has no replacement.

Author: AbhiPrasad

docs/migration/v8-to-v9.md

@@ -107,6 +107,7 @@ It will be removed in a future major version.
 - The `getNumberOfUrlSegments` method has been removed. There is no replacement.
 - The `validSeverityLevels` export has been removed. There is no replacement.
 - The `arrayify` export has been removed. There is no replacement.
+- The `flatten` export has been removed. There is no replacement.
 
 ### `@sentry/nestjs`
 

packages/core/src/utils-hoist/array.ts

@@ -1,6 +1,4 @@
 export { applyAggregateErrorsToEvent } from './aggregate-errors';
-// eslint-disable-next-line deprecation/deprecation
-export { flatten } from './array';
 export { getBreadcrumbLogLevelFromHttpStatusCode } from './breadcrumb-log-level';
 export { getComponentName, getDomElement, getLocationHref, htmlTreeAsString } from './browser';
 export { dsnFromString, dsnToString, makeDsn } from './dsn';

packages/core/src/utils-hoist/index.ts

@@ -95,9 +95,8 @@ export function calculateCacheItemSize(response: unknown): number | undefined {
     : getSize(response);
 }
 
-// TODO(v9): This is inlined from core so we can deprecate `flatten`.
-//           It's usage can be replaced with `Array.flat` in v9.
 type NestedArray<T> = Array<NestedArray<T> | T>;
+
 function flatten<T>(input: NestedArray<T>): T[] {
   const result: T[] = [];
 

packages/core/test/utils-hoist/array.test.ts

@@ -62,7 +62,6 @@ import {
   extractTraceparentData as extractTraceparentData_imported,
   filenameIsInApp as filenameIsInApp_imported,
   fill as fill_imported,
-  flatten as flatten_imported,
   forEachEnvelopeItem as forEachEnvelopeItem_imported,
   generatePropagationContext as generatePropagationContext_imported,
   generateSentryTraceHeader as generateSentryTraceHeader_imported,
@@ -599,10 +598,6 @@ export const isNodeEnv = isNodeEnv_imported;
 /** @deprecated Import from `@sentry/core` instead. */
 export const loadModule = loadModule_imported;
 
-/** @deprecated Import from `@sentry/core` instead. */
-// eslint-disable-next-line deprecation/deprecation
-export const flatten = flatten_imported;
-
 /** @deprecated Import from `@sentry/core` instead. */
 // eslint-disable-next-line deprecation/deprecation
 export const memoBuilder = memoBuilder_imported;