backend-plugin-api: remove WIP permissions from service principal

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/backend-plugin-api/api-report.md

@@ -125,7 +125,6 @@ export type BackstagePrincipalTypes = {
 export type BackstageServicePrincipal = {
   type: 'service';
   subject: string;
-  permissions?: string[];
 };
 
 // @public (undocumented)

packages/backend-plugin-api/src/services/definitions/AuthService.ts

@@ -38,9 +38,6 @@ export type BackstageServicePrincipal = {
 
   // Exact format TBD, possibly 'plugin:<pluginId>' or 'external:<externalServiceId>'
   subject: string;
-
-  // Not implemented in the first iteration, but this is how we might extend this in the future
-  permissions?: string[];
 };
 
 /**