Revert "Documentation for Allow Login using Mobile Number (#8918)"

This reverts commit 818ad397c85eb37266133d194be89ec2cf8164f3.
diff --git a/erpnext/docs/assets/img/setup/users/user-login-email.png b/erpnext/docs/assets/img/setup/users/user-login-email.png
deleted file mode 100644
index 71050af..0000000
--- a/erpnext/docs/assets/img/setup/users/user-login-email.png
+++ /dev/null
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diff --git a/erpnext/docs/assets/img/setup/users/user-login-mobile.png b/erpnext/docs/assets/img/setup/users/user-login-mobile.png
deleted file mode 100644
index 1d7af14..0000000
--- a/erpnext/docs/assets/img/setup/users/user-login-mobile.png
+++ /dev/null
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diff --git a/erpnext/docs/user/manual/en/setting-up/settings/system-settings.md b/erpnext/docs/user/manual/en/setting-up/settings/system-settings.md
index b436b46..053b4f1 100644
--- a/erpnext/docs/user/manual/en/setting-up/settings/system-settings.md
+++ b/erpnext/docs/user/manual/en/setting-up/settings/system-settings.md
@@ -2,8 +2,6 @@
 
 You can localize ERPNext to use particular timezone, date, number or currency format and also set global session expiry via System Settings.
 
-By checking the 'Allow Login using Mobile Number' checkbox, you can login to ERPNext using a valid mobile number set in your User account. 
-
 To open System Settings, go to:
 
 > Setup > Settings > System Settings
diff --git a/erpnext/docs/user/manual/en/setting-up/users-and-permissions/adding-users.md b/erpnext/docs/user/manual/en/setting-up/users-and-permissions/adding-users.md
index 6fb64df..517c674 100644
--- a/erpnext/docs/user/manual/en/setting-up/users-and-permissions/adding-users.md
+++ b/erpnext/docs/user/manual/en/setting-up/users-and-permissions/adding-users.md
@@ -20,10 +20,7 @@
 
 Add user details such as First Name, Last Name, Email etc.
 
-The user's Email will become the user id. Mobile No can also be used to log in if you check the Allow Login using Mobile No checkbox under the Security section in System Settings. While Mobile No will be unique, it will not be treated as a user id.
-
-<img class="screenshot" src="{{docs_base_url}}/assets/img/setup/users/user-login-email.png" alt="Email Login">
-<img class="screenshot" src="{{docs_base_url}}/assets/img/setup/users/user-login-mobile.png" alt="Mobile No Login">
+The user's Email will become the user id.
 
 After adding these details, save the user.