wifi: mac80211: remove tx_handlers_drop debugfs stats

wifi: mac80211: remove tx_handlers_drop debugfs stats

Commit 906a5a8c7152 ("wifi: mac80211: add tx_handlers_drop statistics
to ethtool") added a tx_handlers_drop counter to ethtool stats.
During review [1], Johannes noted that the existing debugfs counter
is now redundant. Remove the debugfs stat to avoid duplication and
streamline statistics reporting.

Link: https://lore.kernel.org/linux-wireless/ce5f2bd899caa2de32f36ce554d9cada073979c0.camel@sipsolutions.net/
Signed-off-by: Sarika Sharma <quic_sarishar@quicinc.com>
Link: https://patch.msgid.link/20250918040846.4032734-1-quic_sarishar@quicinc.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>