ref(flags): don't export FeatureFlagContext in types-hoist/context.ts (#14741)

This isn't exported in types-hoist/index, but we found users can still
import it from a `build/` file. Discussed with @billyvg we don't want
users to accidentally import it this way.

Note we currently use this type in sentry, until
getsentry/sentry#81954 is rolled out.

Author: aliu39

packages/core/src/types-hoist/context.ts

@@ -133,6 +133,6 @@ export interface MissingInstrumentationContext extends Record<string, unknown> {
  * directly is not recommended. Use the functions in @sentry/browser
  * src/utils/featureFlags instead.
  */
-export interface FeatureFlagContext extends Record<string, unknown> {
+interface FeatureFlagContext extends Record<string, unknown> {
   values: FeatureFlag[];
 }