boards: xenvm: Unset HEAP_MEM_POOL_SIZE in gicv3 variant

In HWMv1, the `xenvm` and `xenvm_gicv3` boards used different heap sizes
- 16384 and 0 (default) respectively. Due to HWMv2 defconfig inheritance
the setting must be moved to `Kconfig.defconfig`.

As a result, `xenvm_xenvm_gicv3_defconfig` can be removed, because it is
now equal to `xenvm_defconfig` (base).

Signed-off-by: Grzegorz Swiderski <grzegorz.swiderski@nordicsemi.no>

boards/xen/xenvm/Kconfig.defconfig

@@ -6,4 +6,7 @@ if BOARD_XENVM
 config BUILD_OUTPUT_BIN
 	default y
 
+config HEAP_MEM_POOL_SIZE
+	default 16384 if BOARD_XENVM_XENVM
+
 endif # BOARD_XENVM

boards/xen/xenvm/xenvm_defconfig

@@ -2,7 +2,6 @@
 CONFIG_SERIAL=y
 
 CONFIG_MAX_XLAT_TABLES=24
-CONFIG_HEAP_MEM_POOL_SIZE=16384
 
 # Enable console
 CONFIG_CONSOLE=y

boards/xen/xenvm/xenvm_xenvm_gicv3_defconfig

@@ -1,16 +0,0 @@
-# Enable UART driver
-CONFIG_SERIAL=y
-
-CONFIG_MAX_XLAT_TABLES=24
-
-# Enable console
-CONFIG_CONSOLE=y
-CONFIG_UART_CONSOLE=y
-
-# Enable logging subsys
-CONFIG_LOG=y
-CONFIG_LOG_MODE_MINIMAL=n
-
-CONFIG_USERSPACE=n
-
-CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME=y