d->m: Try too-large PNGs as JPEG for upload

Large PNGs were almost certainly originally JPEG photos that were
converted to PNG by the user copy-pasting.
If the PNG is just supposed to be that large, you can still get the
original through the external URL option.

Had to change _removeExpiryParams to be based on URL parsing instead of
regexp because regexp didn't work with &format=jpeg on the end.

src/d2m/converters/message-to-event.test.js

@@ -1103,6 +1103,45 @@ test("message2event: very large attachment is linked instead of being uploaded",
 	}])
 })
 
+test("message2event: very large png is converted to jpeg for upload", async t => {
+	const events = await messageToEvent({
+		content: "",
+		attachments: [{
+			filename: "855064e9-bdae-487a-a497-c662bd510487.png",
+			url: "https://cdn.discordapp.com/attachments/1160894080998461480/1548656385292509274/855064e9-bdae-487a-a497-c662bd510487.png",
+			proxy_url: "https://media.discordapp.net/attachments/1160894080998461480/1548656385292509274/855064e9-bdae-487a-a497-c662bd510487.png",
+			content_type: "image/png",
+			width: 5472,
+			height: 3648,
+			size: 14967919
+		}]
+	}, data.guild.general, {}, {
+		async fetch(url, init) {
+			t.equal(url, "https://media.discordapp.net/attachments/1160894080998461480/1548656385292509274/855064e9-bdae-487a-a497-c662bd510487.png?format=jpeg")
+			t.equal(init.method, "HEAD")
+			return new Response("wa", {headers: {
+				"Content-Type": "image/jpeg",
+				"Content-Length": 483085
+			}})
+		}
+	})
+	t.deepEqual(events, [{
+		$type: "m.room.message",
+		"m.mentions": {},
+		msgtype: "m.image",
+		body: "855064e9-bdae-487a-a497-c662bd510487.jpg",
+		info: {
+			w: 5472,
+			h: 3648,
+			mimetype: "image/jpeg",
+			size: 483085
+		},
+		external_url: "https://bridge.example.org/download/discordcdn/1160894080998461480/1548656385292509274/855064e9-bdae-487a-a497-c662bd510487.png",
+		filename: "855064e9-bdae-487a-a497-c662bd510487.jpg",
+		url: "mxc://cadence.moe/zXNXRvJwRDMIzZZVqHUXtGeD"
+	}])
+})
+
 test("message2event: multiple attachments are combined into the same event where possible", async t => {
 	const events = await messageToEvent({
 		content: "hey",