doc: remove docs referencing Clear Linux

ACRN 2.1 supports two virtual boot modes, deprivilege boot mode and
direct boot mode. The deprivilege boot mode’s main purpose is to support
booting Clear Linux Service VM with UEFI service support, but this
brings scalability problems when porting ACRN to new Intel platforms.
For the 2.2 release, deprivilege mode is removed, and only direct boot
is supported, and with this we've removed support for Clear Linux as the
service VM, which impacts over 50 ACRN documents.  This PR removes
documents we don't intend to update, and fixes broken links that would
occur from references to these deleted docs.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/develop.rst

@@ -32,9 +32,7 @@ Service VM Tutorials
 .. toctree::
    :maxdepth: 1
 
-   tutorials/using_ubuntu_as_sos
    tutorials/running_deb_as_serv_vm
-   tutorials/cl_servicevm
 
 User VM Tutorials
 *****************
@@ -44,15 +42,12 @@ User VM Tutorials
 .. toctree::
    :maxdepth: 1
 
-   tutorials/building_uos_from_clearlinux
    tutorials/using_windows_as_uos
    tutorials/running_ubun_as_user_vm
    tutorials/running_deb_as_user_vm
    tutorials/using_xenomai_as_uos
-   tutorials/using_celadon_as_uos
    tutorials/using_vxworks_as_uos
    tutorials/using_zephyr_as_uos
-   tutorials/agl-vms
 
 Enable ACRN Features
 ********************
@@ -62,12 +57,9 @@ Enable ACRN Features
 .. toctree::
    :maxdepth: 1
 
-   tutorials/acrn-dm_QoS
-   tutorials/open_vswitch
    tutorials/sgx_virtualization
    tutorials/vuart_configuration
    tutorials/rdt_configuration
-   tutorials/using_sbl_on_up2
    tutorials/waag-secure-boot
    tutorials/enable_s5
    tutorials/cpu_sharing
@@ -89,23 +81,7 @@ Debug
 .. toctree::
    :maxdepth: 1
 
+   tutorials/using_serial_port
    tutorials/debug
    tutorials/realtime_performance_tuning
    tutorials/rtvm_performance_tips
-
-Additional Tutorials
-********************
-
-.. rst-class:: rst-columns2
-
-.. toctree::
-   :maxdepth: 1
-
-   tutorials/up2
-   tutorials/building_acrn_in_docker
-   tutorials/acrn_ootb
-   tutorials/static-ip
-   tutorials/increase-uos-disk-size
-   tutorials/sign_clear_linux_image
-   tutorials/enable_laag_secure_boot
-   tutorials/kbl-nuc-sdc