Remove references to Google+

According to google, this is no longer supported and structured data should be used instead: https://support.google.com/webmasters/answer/6083347?hl=en

docs/content/en/content-management/authors.md

@@ -44,7 +44,6 @@ weight         = 10
 [social]
     facebook   = "alice.allison"
     twitter    = "alice"
-    googleplus = "aliceallison1"
     website    = "www.example.com"
 
 [params]
@@ -108,9 +107,9 @@ You can find a list of all template variables to access the profile information
 
 ### Link Social Network Accounts
 
-As aforementioned, Hugo is able to generate links to profiles of the most popular social networks. The following social networks with their corrersponding identifiers are supported:  `github`, `facebook`, `twitter`, `googleplus`, `pinterest`, `instagram`, `youtube` and `linkedin`.
+As aforementioned, Hugo is able to generate links to profiles of the most popular social networks. The following social networks with their corrersponding identifiers are supported:  `github`, `facebook`, `twitter`, `pinterest`, `instagram`, `youtube` and `linkedin`.
 
-This is can be done with the `.Social.URL` function. Its only parameter is the name of the social network as they are defined in the profile (e.g. `facebook`, `googleplus`). Custom variables like `website` remain as they are.
+This is can be done with the `.Social.URL` function. Its only parameter is the name of the social network as they are defined in the profile (e.g. `facebook`). Custom variables like `website` remain as they are.
 
 Most articles feature a small section with information about the author at the end. Let's create one containing the author's name, a thumbnail, a (summarized) biography and links to all social networks:
 

hugolib/site.go

@@ -672,7 +672,6 @@ func (s *SiteInfo) DisqusShortname() string {
 // facebook_admin
 // twitter
 // twitter_domain
-// googleplus
 // pinterest
 // instagram
 // youtube

resources/page/page_author.go

@@ -36,7 +36,6 @@ type Author struct {
 // - github
 // - facebook
 // - twitter
-// - googleplus
 // - pinterest
 // - instagram
 // - youtube

tpl/tplimpl/embedded/templates.autogen.go

@@ -269,7 +269,7 @@ if (!doNotTrack) {
     {{ end }}
 </ul>
 {{ end }}`},
-	{`schema.html`, `{{ with .Site.Social.GooglePlus }}<link rel="publisher" href="{{ . }}"/>{{ end }}
+	{`schema.html`, `
 <meta itemprop="name" content="{{ .Title }}">
 <meta itemprop="description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end }}">
 

tpl/tplimpl/embedded/templates/schema.html

@@ -1,4 +1,3 @@
-{{ with .Site.Social.GooglePlus }}<link rel="publisher" href="{{ . }}"/>{{ end }}
 <meta itemprop="name" content="{{ .Title }}">
 <meta itemprop="description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end }}">