Remove values that cannot be updated from VolumeSpecUpdate

[lpabon]

Is this a BUG REPORT or FEATURE REQUEST?:
BUG

What happened:
The following values cannot be updated:

// VolumeSpecUpdate provides a method to set any of the VolumeSpec of an existing volume
message VolumeSpecUpdate {
  // Ephemeral storage
  oneof ephemeral_opt { bool ephemeral = 1; }
  // Format specifies the filesystem for this volume.
  oneof format_opt { FSType format = 3; }
  // BlockSize for the filesystem.
  oneof block_size_opt { int64 block_size = 4; }
  // Aggregatiokn level Specifies the number of parts the volume can be aggregated from.
  oneof aggregation_level_opt { uint32 aggregation_level = 13; }
  // Encrypted is true if this volume will be cryptographically secured.
  oneof encrypted_opt { bool encrypted = 14; }
  // GroupEnforced is true if consistency group creation is enforced.
  oneof group_enforced_opt { bool group_enforced = 20; }
  // Compressed is true if this volume is to be compressed.
  oneof compressed_opt { bool compressed = 21; }
  // Cascaded is true if this volume can be populated on any node from an external source.
  oneof cascaded_opt { bool cascaded = 22; }
}