makefile: cleanup comments
makefile: cleanup comments

The commit 7303c02bc2 ("bpf-mock makefile: Remove removed mock target") removed
the bpf-mock-lint target, but there left some comments about running it. Remove
the mentions of bpf-mock.

Signed-off-by: Anton Protopopov <302f9ad3a2e1cbf999e415016f4fb86fd4f39c95@isovalent.com>

cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium