Remove unused `WhisperTextProtocol.proto`

protos/WhisperTextProtocol.proto

@@ -1,28 +0,0 @@
-package signalservice;
-
-option java_package = "org.whispersystems.libsignal.protocol";
-option java_outer_classname = "WhisperProtos";
-
-message WhisperMessage {
-  optional bytes  ephemeralKey    = 1;
-  optional uint32 counter         = 2;
-  optional uint32 previousCounter = 3;
-  optional bytes  ciphertext      = 4; // PushMessageContent
-}
-
-message PreKeyWhisperMessage {
-  optional uint32 registrationId = 5;
-  optional uint32 preKeyId       = 1;
-  optional uint32 signedPreKeyId = 6;
-  optional bytes  baseKey        = 2;
-  optional bytes  identityKey    = 3;
-  optional bytes  message        = 4; // WhisperMessage
-}
-
-message KeyExchangeMessage {
-  optional uint32 id               = 1;
-  optional bytes  baseKey          = 2;
-  optional bytes  ephemeralKey     = 3;
-  optional bytes  identityKey      = 4;
-  optional bytes  baseKeySignature = 5;
-}