RISC-V: defconfigs: Remove redundant K210 DT source

The "k210_generic" DT has been the default in Kconfig since 67d96729
("riscv: Update Canaan Kendryte K210 device tree"), so drop it from the
defconfigs to avoid diff with savedefconfig.
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/configs/nommu_k210_defconfig

@@ -29,7 +29,6 @@ CONFIG_EMBEDDED=y
 CONFIG_SLOB=y
 # CONFIG_MMU is not set
 CONFIG_SOC_CANAAN=y
-CONFIG_SOC_CANAAN_K210_DTB_SOURCE="k210_generic"
 CONFIG_MAXPHYSMEM_2GB=y
 CONFIG_SMP=y
 CONFIG_NR_CPUS=2

arch/riscv/configs/nommu_k210_sdcard_defconfig

@@ -21,7 +21,6 @@ CONFIG_EMBEDDED=y
 CONFIG_SLOB=y
 # CONFIG_MMU is not set
 CONFIG_SOC_CANAAN=y
-CONFIG_SOC_CANAAN_K210_DTB_SOURCE="k210_generic"
 CONFIG_MAXPHYSMEM_2GB=y
 CONFIG_SMP=y
 CONFIG_NR_CPUS=2