configs: stm32h743-eval: Disable CONFIG_NET flag

Network support was never added on this board, disable
CONFIG_NET flag to avoid following warning:

===================== WARNING ======================
This board does not use CONFIG_DM_ETH (Driver Model
for Ethernet drivers). Please update the board to use
CONFIG_DM_ETH before the v2020.07 release. Failure to
update by the deadline may result in board removal.
See doc/driver-model/migration.rst for more info.
====================================================

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/configs/stm32h743-eval_defconfig b/configs/stm32h743-eval_defconfig
index 4d88ed3..e148014 100644
--- a/configs/stm32h743-eval_defconfig
+++ b/configs/stm32h743-eval_defconfig
@@ -24,6 +24,7 @@
 # CONFIG_ISO_PARTITION is not set
 CONFIG_OF_CONTROL=y
 CONFIG_DEFAULT_DEVICE_TREE="stm32h743i-eval"
+# CONFIG_NET is not set
 CONFIG_DM_MMC=y
 CONFIG_STM32_SDMMC2=y
 # CONFIG_PINCTRL_FULL is not set