config: Remove mailbox prompt, no longer used

doc/config.md

@@ -30,7 +30,6 @@ variables it supports:
     INBUCKET_WEB_ADDR                   0.0.0.0:9000        Web server IP4 host:port
     INBUCKET_WEB_UIDIR                  ui                  User interface dir
     INBUCKET_WEB_GREETINGFILE           ui/greeting.html    Home page greeting HTML
-    INBUCKET_WEB_MAILBOXPROMPT          @inbucket           Prompt next to mailbox input
     INBUCKET_WEB_MONITORVISIBLE         true                Show monitor tab in UI?
     INBUCKET_WEB_MONITORHISTORY         30                  Monitor remembered messages
     INBUCKET_WEB_PPROF                  false               Expose profiling tools on /debug/pprof
@@ -309,18 +308,6 @@ Inbucket installation, as well as link to REST documentation, etc.
 
 - Default: `ui/greeting.html`
 
-### Mailbox Prompt
-
-`INBUCKET_WEB_MAILBOXPROMPT`
-
-Text prompt displayed to the right of the mailbox name input field in the web
-interface.  Can be used to nudge your users into typing just the mailbox name
-instead of an entire email address.
-
-Set to an empty string to hide the prompt.
-
-- Default: `@inbucket`
-
 ### Monitor Visible
 
 `INBUCKET_WEB_MONITORVISIBLE`

pkg/config/config.go

@@ -95,7 +95,6 @@ type Web struct {
 	Addr           string `required:"true" default:"0.0.0.0:9000" desc:"Web server IP4 host:port"`
 	UIDir          string `required:"true" default:"ui" desc:"User interface dir"`
 	GreetingFile   string `required:"true" default:"ui/greeting.html" desc:"Home page greeting HTML"`
-	MailboxPrompt  string `required:"true" default:"@inbucket" desc:"Prompt next to mailbox input"`
 	MonitorVisible bool   `required:"true" default:"true" desc:"Show monitor tab in UI?"`
 	MonitorHistory int    `required:"true" default:"30" desc:"Monitor remembered messages"`
 	PProf          bool   `required:"true" default:"false" desc:"Expose profiling tools on /debug/pprof"`