MM-22710: Bump golangci to 1.23.6 (#13948)

* MM-22710: Bump golangci to 1.23.6

This is to prepare the codebase for 1.14 shift.

1.23.6 has some fixes which is necessary for a codebase using Go 1.14.

* Remove golangci service

The service is getting shut down.
https://medium.com/golangci/golangci-com-is-closing-d1fc1bd30e0e

* Remove unneeded comment

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

build/Jenkinsfile.pr

@@ -103,7 +103,7 @@ pipeline {
 						sh """
 							cd /go/src/github.com/mattermost/mattermost-server
 							echo "Installing golangci-lint"
-							curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh| sh -s -- -b /usr/local/bin v1.23.3 # Keep this in sync with .golangci.yml and .circleci/config.yml
+							curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh| sh -s -- -b /usr/local/bin v1.23.6 # Keep this in sync with .circleci/config.yml
 							echo "Installing mattermost-govet"
 							GO111MODULE=off go get -u github.com/mattermost/mattermost-govet
 							export PATH=$PATH:$GOBIN