user-docs/install_aem.md: Remove unencrypted drive instructions

Instructions for reinstalling grub2 on Legacy systems.
AEM without encryption is pretty much useless anyway.

Signed-off-by: Filip Gołaś <filip.golas@3mdeb.com>

Author: philipanda

docs/user-docs/install_aem.md

@@ -110,21 +110,10 @@ sudo qubes-dom0-update --disablerepo="*" --enablerepo=aem --action=reinstall \
 ###### Updating GRUB on legacy systems
 
 Booting on legacy systems requires manual installation of GRUB2 to the MBR
-of disk where Qubes OS is stored. In the example below it is `/dev/sda`,
-yours may be different.
+of disk where Qubes OS is stored. If you are sure where the root partition
+is located, you can skip the following steps explaining how to find it out.
 
-To check on which partition is your OS installed, if the disk is not encrypted,
-run:
-
-```bash
-df --output=source /
-```
-
-If your disk is encrypted, then the command above will print a filename
-like `/dev/mapper/...`. This is an LVM Logical Volume and finding out the
-physical disk on which the root partition resides takes a couple steps.
-If you are sure where the root partition is located, you can skip the steps to
-find it out.
+To check on which drive is your OS installed, run:
 
 1. Get the Logical Volume (LV) file: