Revert "Consider root and current section's content type if set in front matter"

This reverts commit c790029e1d.

hugolib/site_sections_test.go

@@ -176,8 +176,6 @@ PAG|{{ .Title }}|{{ $sect.InSection . }}
 			active, err := home.InSection(home)
 			assert.NoError(err)
 			assert.True(active)
-			assert.Equal(p, p.FirstSection())
-
 		}},
 		{"l1", func(p *Page) {
 			assert.Equal("L1s", p.title)
@@ -252,8 +250,6 @@ PAG|{{ .Title }}|{{ $sect.InSection . }}
 			assert.NoError(err)
 			assert.False(isAncestor)
 
-			assert.Equal(l1, p.FirstSection())
-
 		}},
 		{"perm a,link", func(p *Page) {
 			assert.Equal("T9_-1", p.title)