doc: environment: Drop u-boot_addr_r

This variable is never set nor explained why it would be set, drop it.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst
index 28a8952..a3f23d4 100644
--- a/doc/usage/environment.rst
+++ b/doc/usage/environment.rst
@@ -390,7 +390,6 @@
 ================= ============== ================ ==============
 Image             File Name      RAM Address      Flash Location
 ================= ============== ================ ==============
-u-boot            u-boot         u-boot_addr_r    u-boot_addr
 Linux kernel      bootfile       kernel_addr_r    kernel_addr
 device tree blob  fdtfile        fdt_addr_r       fdt_addr
 ramdisk           ramdiskfile    ramdisk_addr_r   ramdisk_addr