tests: drivers: dma: clean-up conf for silabs boards

With the recent upgrade of the LDMA driver, these conf files are no
longer needed. (The LDMA driver now supports channel allocation and
large transfers)

Signed-off-by: Martin Hoff <martin.hoff@silabs.com>

Author: Martinhoff-maker

tests/drivers/dma/loop_transfer/boards/sltb010a.conf

@@ -1,5 +1,4 @@
 # Copyright (c) 2024 Silicon Laboratories, Inc.
 # SPDX-License-Identifier: Apache-2.0
 
-CONFIG_DMA_LOOP_TRANSFER_CHANNEL_NR=0
 CONFIG_DMA_LOOP_TRANSFER_SIZE=2048

tests/drivers/dma/loop_transfer/boards/slwrb4180a.conf

@@ -1,5 +1,4 @@
 # Copyright (c) 2024 Silicon Laboratories, Inc.
 # SPDX-License-Identifier: Apache-2.0
 
-CONFIG_DMA_SG_CHANNEL_NR=0
 CONFIG_DMA_SG_XFER_SIZE=4096