Remove cross-fetch and isomorphic-form-data

[jimmywarting]

sdk-for-web/package.json

Lines 34 to 37 in 7b37a2b

	"dependencies": {
	"cross-fetch": "3.1.5",
	"isomorphic-form-data": "2.0.0"
	},

formdata + fetch is built-in to all evergreen env. (NodeJS v18+)
if it isn't just let the developer who depend on this package bring them in themself if they need to.

[SayyamJain101]

Can you assign me this issue @jimmywarting