Remove redundant h1 titles using # syntax

https://github.com/QubesOS/qubes-issues/issues/6701#issuecomment-862060759

user/downloading-installing-upgrading/custom-install.md

@@ -8,7 +8,6 @@ ref: 152
 title: Custom Installation
 ---
 
-# Custom Installation
 
 In the present context, "custom installation" refers to things like manual partitioning, setting up LVM and RAID, and manual LUKS encryption configuration.
 

user/downloading-installing-upgrading/install-security.md

@@ -10,7 +10,6 @@ ref: 149
 title: Installation security
 ---
 
-# Installation security
 
 There are several security matters to consider before and during the Qubes installation process.
 

user/downloading-installing-upgrading/supported-versions.md

@@ -7,7 +7,6 @@ ref: 154
 title: Supported Versions
 ---
 
-# Supported Versions
 
 This page details the level and period of support for versions of operating systems in the Qubes ecosystem.
 

user/downloading-installing-upgrading/upgrade/upgrade-to-r3_0.md

@@ -10,7 +10,6 @@ ref: 159
 title: Upgrading to R3.0
 ---
 
-# Upgrading Qubes R2 to R3.0
 
 **This instruction is highly experimental, the official way to upgrade from R2 is to backup the data and reinstall the system. Use at your own risk!**
 

user/downloading-installing-upgrading/upgrade/upgrade-to-r3_1.md

@@ -10,7 +10,6 @@ ref: 155
 title: Upgrading to R3.1
 ---
 
-# Upgrading Qubes R3.0 to R3.1
 
 **Before attempting either an in-place upgrade or a clean installation, we
 strongly recommend that users [back up their systems](/doc/backup-restore/).**

user/downloading-installing-upgrading/upgrade/upgrade-to-r3_2.md

@@ -10,7 +10,6 @@ ref: 161
 title: Upgrading to R3.2
 ---
 
-# Upgrading Qubes R3.1 to R3.2
 
 **Before attempting either an in-place upgrade or a clean installation, we
 strongly recommend that users [back up their systems](/doc/backup-restore/).**