doc: Remove the patman documentation

The full patman manual now lives with the standalone patch-manager
package, making the 1000-line copy in the tree redundant.

Remove the in-tree manual, its README and the doc/develop/patman.rst
toctree page.

The sending-patches guide already introduces patman, so point it at the
patch-manager package instead of the now-dead ':doc:' cross-reference
and, with the manual gone, add a couple of lines on how the tool works.
Point the SPI howto at that guide too, rather than repeating the install
details.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>

doc/develop/driver-model/spi-howto.rst

@@ -649,8 +649,8 @@ board.
 Prepare patches and send them to the mailing lists
 --------------------------------------------------
 
-You can use 'tools/patman/patman' to prepare, check and send patches for
-your work. See tools/patman/README for details.
+You can prepare, check and send patches for your work using the tools described
+in :doc:`/develop/sending_patches`.
 
 A little note about SPI uclass features
 ---------------------------------------

doc/develop/index.rst

@@ -16,7 +16,6 @@ General
    docstyle
    kconfig
    memory
-   patman
    process
    release_cycle
    security

doc/develop/patman.rst

@@ -1 +0,0 @@
-../../tools/patman/patman.rst

doc/develop/sending_patches.rst

@@ -73,9 +73,15 @@ Using patman
 
 You can use a tool called patman to prepare, check and send patches. It creates
 change logs, cover letters and patch notes. It also simplifies the process of
-sending multiple versions of a series.
+sending multiple versions of a series. patman is driven by tags in your commit
+messages, and can collect Reviewed-by and other tags from patchwork when you
+send a new version. It can optionally keep a local database of all your series,
+tracking each version and their review / applied status over time, so you can
+easily track upstreaming progress.
 
-See more details at :doc:`patman`.
+patman now lives outside the U-Boot tree; install it with
+``pip install patch-manager``. See the
+`patman documentation <https://deinde.dev/patman>`_ for details.
 
 General Patch Submission Rules
 ------------------------------