While fixing kernel-doc issues it was discovered that the
ieee80211_set_hw_80211_encap() prototype doesn't actually have an
implementation, so remove it.

Note the implementation was removed in commit 6aea26ce ("mac80211:
rework tx encapsulation offload API").
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://msgid.link/20240329-mac80211-kdoc-retval-v1-1-5e4d1ad6c250@quicinc.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>