esp32/boards: Remove all IDF3 variants.

IDF 3 builds are very old now (it seems like the last successful builds are
from 2021), and the current IDF 5 is stable.  So remove IDF 3 variants.
Signed-off-by: Matt Trentini <matt.trentini@gmail.com>

ports/esp32/boards/ESP32_GENERIC/board.json

@@ -16,7 +16,6 @@
     "thumbnail": "",
     "url": "https://www.espressif.com/en/products/modules",
     "variants": {
-        "IDF3": "Compiled with IDF 3.x",
         "D2WD": "ESP32 D2WD",
         "SPIRAM": "Support for SPIRAM / WROVER",
         "UNICORE": "ESP32 Unicore",

ports/esp32/boards/UM_TINYPICO/board.json

@@ -22,8 +22,5 @@
     "product": "TinyPICO",
     "thumbnail": "",
     "url": "https://www.tinypico.com/",
-    "variants": {
-        "IDF3": "Compiled with IDF 3.x"
-    },
     "vendor": "Unexpected Maker"
 }

tools/autobuild/build-boards.sh

@@ -55,10 +55,8 @@ function build_board {
     $MICROPY_AUTOBUILD_MAKE BOARD=$board BUILD=$build_dir && copy_artefacts $dest_dir $descr $fw_tag $build_dir $@
     rm -rf $build_dir
 
-    # Query variants from board.json and build them. Ignore the special "IDF3"
-    # variant for ESP32 boards (this allows the downloads page to still have
-    # the idf3 files for older releases that used to be explicitly built).
-    for variant in `cat $board_json | python3 -c "import json,sys; print(' '.join(v for v in json.load(sys.stdin).get('variants', {}).keys() if v != 'IDF3'))"`; do
+    # Query variants from board.json and build them.
+    for variant in `cat $board_json | python3 -c "import json,sys; print(' '.join(json.load(sys.stdin).get('variants', {}).keys()))"`; do
         local variant_build_dir=$build_dir-$variant
         echo "building variant $descr $board $variant"
         $MICROPY_AUTOBUILD_MAKE BOARD=$board BOARD_VARIANT=$variant BUILD=$variant_build_dir && copy_artefacts $dest_dir $descr-$variant $fw_tag $variant_build_dir $@