bpf: use the default asm_named_section target hook

bpf: use the default asm_named_section target hook

This patch makes the BPF backend to not provide its own implementation
of the asm_named_section hook; the default handler works perfectly
well.

2020-09-02  Jose E. Marchesi  <jose.marchesi@oracle.com>

	gcc/
	* config/bpf/bpf.c (bpf_asm_named_section): Delete.
	(TARGET_ASM_NAMED_SECTION): Likewise.