esp32: Restore ESP32-C3 brownout detector settings to IDF defaults.

Commit a66bd7a4 added the
ESP32_GENERIC_C3_USB board (now merged with ESP32_GENERIC_C3) and changed
the brownout detector from the default level 7 (~2.51V) to level 4
(~2.92V).

Raising the level again seems to fix random BOD resets on some of the
cheaper ESP32-C3 dev boards (that likely skimp on power supply
capacitance).

Specifically, this change prevents random resets running multi_bluetooth
tests on ESP32-C3 "SuperMini" board.

Also removed from the LOLIN_C3_MINI board as it seems this config is a copy
of the generic one.

This work was funded through GitHub Sponsors.
Signed-off-by: Angus Gratton <angus@redyak.com.au>

ports/esp32/boards/ESP32_GENERIC_C3/sdkconfig.c3usb

 CONFIG_ESP32C3_REV_MIN_3=y
-CONFIG_ESP32C3_BROWNOUT_DET=y
-CONFIG_ESP32C3_BROWNOUT_DET_LVL_SEL_7=
-CONFIG_ESP32C3_BROWNOUT_DET_LVL_SEL_4=y
-CONFIG_ESP32C3_BROWNOUT_DET_LVL=4

ports/esp32/boards/LOLIN_C3_MINI/sdkconfig.board

 CONFIG_ESP32C3_REV_MIN_3=y
-CONFIG_ESP32C3_BROWNOUT_DET=y
-CONFIG_ESP32C3_BROWNOUT_DET_LVL_SEL_7=
-CONFIG_ESP32C3_BROWNOUT_DET_LVL_SEL_4=y
-CONFIG_ESP32C3_BROWNOUT_DET_LVL=4