[MM-51274] Remove deprecated PermissionUseSlashCommands (#22819)

Co-authored-by: Mattermost Build <build@mattermost.com>

server/model/role.go

@@ -755,7 +755,6 @@ func MakeDefaultRoles() map[string]*Role {
 			PermissionEditPost.Id,
 			PermissionCreatePost.Id,
 			PermissionUseChannelMentions.Id,
-			PermissionUseSlashCommands.Id,
 		},
 		SchemeManaged: true,
 		BuiltIn:       true,
@@ -774,7 +773,6 @@ func MakeDefaultRoles() map[string]*Role {
 			PermissionGetPublicLink.Id,
 			PermissionCreatePost.Id,
 			PermissionUseChannelMentions.Id,
-			PermissionUseSlashCommands.Id,
 			PermissionManagePublicChannelProperties.Id,
 			PermissionDeletePublicChannel.Id,
 			PermissionManagePrivateChannelProperties.Id,