ANDROID: riscv: configs: drop unused spacemit_k1x.fragment

The K1 board build references the fragment that lives in
devices/spacemit/bananapi_f3/spacemit_k1x.fragment via the bazel
target's pre_defconfig_fragments label (BUILD.bazel:329 ":spacemit_k1x.fragment").
The copy under common/arch/riscv/configs/ was a leftover of the initial
import from the vendor BSP and is never read by the build — every
edit to it was dead code.

Delete it. The active fragment in devices/spacemit/bananapi_f3/ has
been updated to enable the symbols introduced in the recent driver
commits (NVMEM_SPACEMIT_EFUSE, SPACEMIT_SOCINFO, POWER_RESET_SPACEMIT_K1X).

Change-Id: I0cf4cf39bc1589668a1e880c25ee3368cf4f2301
Signed-off-by: Guillaume La Roque <glaroque@baylibre.com>

Author: glaroque