iw: drop TX power patch that is part of upstream version now

Applying it again was resulting in duplicated TX info like:
Interface wlan0
        ifindex 6
        wdev 0x1
        addr 00:23:6a:a3:7d:00
        ssid LEDE2
        type AP
        wiphy 0
        channel 11 (2462 MHz), width: 20 MHz, center1: 2462 MHz
        txpower 31.00 dBm
        txpower 31.00 dBm

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

package/network/utils/iw/patches/300-display_interface_TX_power.patch

@@ -1,30 +0,0 @@
-From: =?utf-8?q?Rafa=C5=82_Mi=C5=82ecki?= <zajec5@gmail.com>
-Date: Tue, 1 Sep 2015 09:55:52 +0200
-Subject: iw: display interface TX power if available
-MIME-Version: 1.0
-Content-Type: text/plain; charset="utf-8"
-Content-Transfer-Encoding: 8bit
-
-Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
-[print dBm]
-Signed-off-by: Johannes Berg <johannes.berg@intel.com>
----
- interface.c | 7 +++++++
- 1 file changed, 7 insertions(+)
-
---- a/interface.c
-+++ b/interface.c
-@@ -441,6 +441,13 @@ static int print_iface_handler(struct nl
- 		       indent, txp / 100, txp % 100);
- 	}
- 
-+	if (tb_msg[NL80211_ATTR_WIPHY_TX_POWER_LEVEL]) {
-+		uint32_t txp = nla_get_u32(tb_msg[NL80211_ATTR_WIPHY_TX_POWER_LEVEL]);
-+
-+		printf("%s\ttxpower %d.%.2d dBm\n",
-+		       indent, txp / 100, txp % 100);
-+	}
-+
- 	return NL_SKIP;
- }
-