fix: update validator manager mock and remove staging md files

- Add missing SessionPeriod and SessionOffset to mock Config
- Remove staging-chainspec.md and staging-raw.md files
- Fix CI compilation error for validator manager tests

Author: CorruptedAesthetic

chainspecs/staging/staging-chainspec.md

@@ -136,6 +136,8 @@ impl pallet_validator_manager::Config for Test {
     type RuntimeEvent = RuntimeEvent;
     type PrivilegedOrigin = frame_system::EnsureRoot<AccountId>;
     type MinAuthorities = MinAuthorities;
+    type SessionPeriod = ConstU32<20>; // 20 blocks per session for testing
+    type SessionOffset = ConstU32<0>;  // No offset for testing
     type ValidatorOf = crate::ValidatorOf<Test>;
     type WeightInfo = ();
 }