all: Remove query-variants make target.

This is difficult to implement on cmake-based ports, and having the list
of variants in mpconfigboard.{cmake,mk} duplicates information that's
already in board.json.

This removes the existing query-variants make target from stm32 & rp2
and the definition of BOARD_VARIANTS from the various board files.

Also renames the cmake variable to MICROPY_BOARD_VARIANT to match other
variables such as MICROPY_BOARD. The make variable stays as
BOARD_VARIANT.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

py/mkrules.cmake

@@ -178,7 +178,7 @@ if(MICROPY_FROZEN_MANIFEST)
         set(MICROPY_LIB_DIR ${MICROPY_DIR}/lib/micropython-lib)
     endif()
 
-    if(ECHO_SUBMODULES OR ECHO_QUERY_VARIANTS)
+    if(ECHO_SUBMODULES)
         # No-op, we're just doing submodule/variant discovery.
         # Note: All the following rules are safe to run in discovery mode even
         # though the submodule might not be available as they do not directly depend
@@ -223,9 +223,3 @@ if(ECHO_SUBMODULES)
     execute_process(COMMAND ${CMAKE_COMMAND} -E echo "GIT_SUBMODULES=${GIT_SUBMODULES}")
     message(FATAL_ERROR "Done")
 endif()
-
-# Display BOARD_VARIANTS
-if(ECHO_BOARD_VARIANTS)
-    execute_process(COMMAND ${CMAKE_COMMAND} -E echo "BOARD_VARIANTS=${BOARD_VARIANTS}")
-    message(FATAL_ERROR "Done")
-endif()