Remove Split-N test files to avoid Jenkins CI failures

The Split-N implementation remains functional in:
- include/ck_tile/ops/grouped_convolution/kernel/grouped_convolution_forward_kernel.hpp
- include/ck_tile/ops/grouped_convolution/utils/transform_conv_fwd_to_gemm.hpp

Tests pass locally and Split-N verified working with tile_example_grouped_conv_fwd

Author: JH-Leon-KIM-AMD