Revert "Add micro-kernel to compute FP16 GEMV"

This reverts commit cddf991a

The existing FP16 GEMM micro-kernel (matmul_clamp_f16_f16_f16p16x1biasf16_1x16x8_neon_mla) has a dedicated path for M=1 (a "GEMV" operation).

Signed-off-by: Jakub Sujak <jakub.sujak@arm.com>