Revert "users: Retain authorized_keys file permissions"

With fixed fsreplace1 we don't need to call `sed` any more.
cockpit.file.modify() already reads the tag and passes it to fsreplace1,
so no further changes are necessary.

This partially reverts commit a369480 (but of
course keeps the integration test). Adjust the test as our file.modify()
doesn't append an extra empty line.

pkg/users/authorized-keys.js

@@ -114,12 +114,24 @@ function AuthorizedKeys (user_name, home_dir) {
                 });
     };
 
-    // don't use cockpit.file.modify() here, as that doesn't preserve permissions
-    // (https://github.com/cockpit-project/cockpit/issues/18033)
-    self.remove_key = key => cockpit.spawn(
-        ["sed", "-i", "\\!^" + key + "$!d", filename],
-        { superuser: "try", err: "message" }
-    );
+    self.remove_key = function(key) {
+        return file.modify(function(content) {
+            let lines = null;
+            const new_lines = [];
+
+            if (!content)
+                return "";
+
+            lines = content.trim().split('\n');
+            for (let i = 0; i < lines.length; i++) {
+                if (lines[i] === key)
+                    key = undefined;
+                else
+                    new_lines.push(lines[i]);
+            }
+            return new_lines.join("\n");
+        });
+    };
 
     self.close = function() {
         if (watch)

test/verify/check-shell-keys

@@ -131,7 +131,7 @@ class TestKeys(testlib.MachineCase):
         b.wait_not_in_text("#account-authorized-keys", "Invalid key")
         b.wait_js_func("ph_count_check", "#account-authorized-keys-list tr", 1)
         data = m.execute("cat /home/user/.ssh/authorized_keys")
-        self.assertEqual(data, KEY + "\n\n")
+        self.assertEqual(data, KEY + "\n")
         # Permissions are still ok
         check_perms()
         b.logout()