godoc: remove unused CLI-only identifiers

This is a followup to CL 141397, which removed CLI support from the
godoc command for golang/go#25443. This change removes a few more
CLI-related fields from Presentation type, which are now unused.

It also removes the unused and no longer documented (since CL 143077)
NoHTML PageInfoMode.

Updates golang/go#25443

Change-Id: Ia4147515052889570e2f050e3c2394689d3c5d6c
Reviewed-on: https://go-review.googlesource.com/c/162982
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Agniva De Sarker <agniva.quicksilver@gmail.com>

godoc/pres.go

@@ -47,13 +47,6 @@ type Presentation struct {
 	ShowPlayground bool
 	DeclLinks      bool
 
-	// SrcMode outputs source code instead of documentation in command-line mode.
-	SrcMode bool
-	// HTMLMode outputs HTML instead of plain text in command-line mode.
-	HTMLMode bool
-	// AllMode includes unexported identifiers in the output in command-line mode.
-	AllMode bool
-
 	// NotesRx optionally specifies a regexp to match
 	// notes to render in the output.
 	NotesRx *regexp.Regexp

godoc/server.go

@@ -356,7 +356,6 @@ const (
 	NoFiltering PageInfoMode = 1 << iota // do not filter exports
 	AllMethods                           // show all embedded methods
 	ShowSource                           // show source code, do not extract documentation
-	NoHTML                               // show result in textual form, do not generate HTML
 	FlatDir                              // show directory in a flat (non-indented) manner
 	NoTypeAssoc                          // don't associate consts, vars, and factory functions with types
 )
@@ -366,7 +365,6 @@ var modeNames = map[string]PageInfoMode{
 	"all":     NoFiltering,
 	"methods": AllMethods,
 	"src":     ShowSource,
-	"text":    NoHTML,
 	"flat":    FlatDir,
 }