intl [nfc]: Clean some bitrot in messages_en.json (messages not in the UI)

Using my draft of a tool for finding these, in zulip#5476.

Author: chrisbobbe

static/translations/messages_en.json

@@ -121,7 +121,6 @@
   "Why not start the conversation?": "Why not start the conversation?",
   "That conversation doesn't seem to exist.": "That conversation doesn't seem to exist.",
   "Request timed out.": "Request timed out.",
-  "Chat": "Chat",
   "Sign in with {method}": "Sign in with {method}",
   "Invalid input": "Invalid input",
   "Please enter a URL.": "Please enter a URL.",
@@ -163,23 +162,19 @@
   "Open links with in-app browser": "Open links with in-app browser",
   "Language": "Language",
   "Arabic": "Arabic",
-  "Bokmål": "Bokmål",
   "Bulgarian": "Bulgarian",
   "Catalan": "Catalan",
   "Chinese (China)": "Chinese (China)",
   "Chinese (Taiwan)": "Chinese (Taiwan)",
-  "Croatian": "Croatian",
   "Czech": "Czech",
   "Danish": "Danish",
   "Dutch": "Dutch",
   "English": "English",
   "English (U.K.)": "English (U.K.)",
-  "English (U.S.)": "English (U.S.)",
   "Finnish": "Finnish",
   "French": "French",
   "Galician": "Galician",
   "German": "German",
-  "Greek": "Greek",
   "Hindi": "Hindi",
   "Hungarian": "Hungarian",
   "Indonesian": "Indonesian",
@@ -202,7 +197,6 @@
   "Tamil": "Tamil",
   "Turkish": "Turkish",
   "Ukrainian": "Ukrainian",
-  "Uzbek": "Uzbek",
   "Vietnamese": "Vietnamese",
   "Welsh": "Welsh",
   "Topic": "Topic",
@@ -227,25 +221,18 @@
   "(This user has been deactivated)": "(This user has been deactivated)",
   "(unknown user)": "(unknown user)",
   "Forgot password?": "Forgot password?",
-  "Members": "Members",
   "Recipients": "Recipients",
   "Delete message": "Delete message",
   "Notifications when online": "Notifications when online",
   "Notifications when offline": "Notifications when offline",
   "Stream notifications": "Stream notifications",
-  "Unread": "Unread",
-  "Subscribed": "Subscribed",
   "No users found": "No users found",
   "No streams found": "No streams found",
   "Diagnostics": "Diagnostics",
-  "Toggle compose tools": "Toggle compose tools",
   "Legal": "Legal",
-  "Terms of service": "Terms of service",
-  "Privacy policy": "Privacy policy",
   "Timing": "Timing",
   "Variables": "Variables",
   "Storage": "Storage",
-  "Mark as read": "Mark as read",
   "Mark all as read": "Mark all as read",
   "Mark stream as read": "Mark stream as read",
   "Mark topic as read": "Mark topic as read",
@@ -286,9 +273,6 @@
   "show": "show",
   "hide": "hide",
   "Debug": "Debug",
-  "Render messages with HTML": "Render messages with HTML",
-  "Distinguish unread messages": "Distinguish unread messages",
-  "Split message text": "Split message text",
   "Administrators": "Administrators",
   "Normal users": "Normal users",
   "Share image": "Share image",
@@ -300,23 +284,16 @@
   "Create": "Create",
   "Privacy": "Privacy",
   "Public": "Public",
-  "Private": "Private",
   "Notifications": "Notifications",
   "Stream": "Stream",
   "Private Message": "Private Message",
-  "Muted topics": "Muted topics",
   "Edit stream": "Edit stream",
   "OK": "OK",
   "Please share the image from your browser": "Please share the image from your browser",
   "Share failed": "Share failed",
   "Download complete": "Download complete",
-  "Download file": "Download file",
   "Save": "Save",
   "Pinned": "Pinned",
-  "Pin": "Pin",
-  "Active": "Active",
-  "Idle": "Idle",
-  "Offline": "Offline",
   "Mark messages as read on scroll": "Mark messages as read on scroll",
   "When scrolling through messages, should they automatically be marked as read?": "When scrolling through messages, should they automatically be marked as read?",
   "Always": "Always",
@@ -328,7 +305,6 @@
   "Subscribe": "Subscribe",
   "Unsubscribe": "Unsubscribe",
   "Set yourself to away": "Set yourself to away",
-  "Clear": "Clear",
   "Reactions": "Reactions",
   "No reactions": "No reactions",
   "See who reacted": "See who reacted",
@@ -362,7 +338,6 @@
   "Oops! Something went wrong.": "Oops! Something went wrong.",
   "Uploading {fileName}...": "Uploading {fileName}...",
   "Failed to upload file: {fileName}": "Failed to upload file: {fileName}",
-  "Attachment": "Attachment",
   "Attachment {num}": "Attachment {num}",
   "Failed to mark topic as read": "Failed to mark topic as read",
   "Search topics": "Search topics",