[FAB-4582] Fix gossip proto comments

The gossip proto file has the following section for channel_mac:

    // channel_MAC is an authentication code that proves
    // that the peer that sent this message knows
    // the name of the channel.
    // The channel name that this message relates to
    // can only be computed by a peer that has joined
    // the channel

This is a bit misleading since the name of the channel can be computed by
dictionary attacks where the name of the channel is guessed,
and also by simply knowing the name of the channel beforehand.

Change-Id: I7050ac4e814609b0307ec5b573cf7a84d2a80d24
Signed-off-by: Yacov Manevich <[email protected]>

protos/gossip/message.proto

@@ -126,9 +126,6 @@ message StateInfo {
     // channel_MAC is an authentication code that proves
     // that the peer that sent this message knows
     // the name of the channel.
-    // The channel name that this message relates to
-    // can only be computed by a peer that has joined
-    // the channel
     bytes channel_MAC  = 4;
 }
 
@@ -143,9 +140,6 @@ message StateInfoPullRequest {
     // channel_MAC is an authentication code that proves
     // that the peer that sent this message knows
     // the name of the channel.
-    // The channel name that this message relates to
-    // can only be computed by a peer that has joined
-    // the channel
     bytes channel_MAC  = 1;
 }