boards: wemos: adopt new zephyr:board directive and role

This updates the documentation of all the Wemos boards to use
the new `zephyr:board::` directive.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

boards/wemos/esp32s2_lolin_mini/doc/index.rst

@@ -1,7 +1,4 @@
-.. _esp32s2_lolin_mini:
-
-ESP32-S2 Lolin Mini
-###################
+.. zephyr:board:: esp32s2_lolin_mini
 
 Overview
 ********
@@ -30,10 +27,6 @@ The features include the following:
   - DAC
   - LED PWM with up to 8 channels
 
-.. figure:: img/esp32_s2_lolin_mini.jpg
-        :align: center
-        :alt: ESP32-S2 LOLIN MINI
-
 System requirements
 *******************