Update bsnes from upstream and skip CX4 firmware check

[AkiteruSDA]

Just the couple of emulation-related commits from upstream:

• 7d5aa1e656b9171524d01b1b22917197d8121cb4: fix horizontal offset in high-resolution offset-by-tile mode
• 78474e5d39f58872dc21aca18cf9eb583b147fe7: CX4: Remove extra cycle on DMA to internal RAM (fixes excessive slowdown in Morph Moth fight)

I also realized the new core includes the CX4 firmware already, so there isn't much need to check for the firmware file. I considered updating the old bsnes core to include it as well, but didn't want to mess with things too much, especially for an old core.

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[Morilli]

I also realized the new core includes the CX4 firmware already

Seems you're right about that, I wonder why the core even requests that firmware file in the first place then. Given that the data rom is supposedly math tables only I doubt there's different revisions either.

[AkiteruSDA]

Upstream seems to still check for hg51bs169.data.rom but silently falls back on the built in data ROM if not provided. I figure that's where the request comes from. There is only one version of the data ROM, so not sure how much of a difference that makes, but I tweaked the frontend to still allow for a firmware file just to match upstream's behaviour.