Remove pointOfSaleReceipts feature flag

[iamgabrielma]

Description

Cleans up feature flag service by removing pointOfSaleReceipts, which has been in production for a while.

Testing info

Sending receipts should work normally. For more granular testing:

• Add a breakpoint in POSReceiptService.sendReceipt(...)
• In a store with WC10+, process a transaction and attempt to send a receipt. Observe that we land in receiptsRemote.sendPOSReceipt()
• Update POSReceiptEligibilityConstants.wcPluginMinimumVersion to something like "15.0.0"
• Process a transaction and attempt to send a receipt. Observe that we land in receiptsRemote.sendReceipt() instead.

[iamgabrielma]

AFAU we have no reason for this to be nil, since it's either eligible or it isn't. Also allows to simplify the value we pass to the catch block and the track event.

[joshheald]

Previously, if there was no order, or orderService.updatePOSOrder threw an error, we'd track the receiptEmailFailed event without eligible_for_pos_receipt (thanks to the compactMapValues.)

Now we'll log it as false even if the real answer would have been true.

Perhaps we should just set the isEligible at the top instead of after updating the order. The only thing it uses is the siteID, which isn't going to change from the order update, surely.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS Prototype by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS Prototype
	Build Number	pr16103-08ece84
	Version	23.2
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	08ece84
	Installation URL	2ptaaii0abt98

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[joshheald]

Thanks for cleaning this up. One point about analytics changes this'll cause though...

[joshheald]

Previously, if there was no order, or orderService.updatePOSOrder threw an error, we'd track the receiptEmailFailed event without eligible_for_pos_receipt (thanks to the compactMapValues.)

Now we'll log it as false even if the real answer would have been true.

Perhaps we should just set the isEligible at the top instead of after updating the order. The only thing it uses is the siteID, which isn't going to change from the order update, surely.