perf: optimize NFTDescriptor contract

[smol-ninja]

Changelog

• Closes Fix tokenURI function and remove backwards compatility #1112
• Closes Change contract address and expected token URI strings in tests #1071
• Removed redundant code that is no longer required due to non-compatible nature of NFTDescriptor contract

@andreivladbrg this PR is built on top of #1108. There was an another issue due to which tokenURI was returning ERC20 instead of DAI (comment). All issues have been fixed in this PR.

I recommend that we close #1108 in favour of this PR. I have also added you as the co-author in this.

Previews

Click to see result of tokenURI

{
  "attributes": [
    {
      "trait_type": "Token",
      "value": "DAI"
    },
    {
      "trait_type": "Sender",
      "value": "0x6332e7b1deb1f1a0b77b2bb18b144330c7291bca"
    },
    {
      "trait_type": "Status",
      "value": "Streaming"
    }
  ],
  "description": "This NFT represents a stream in Sablier Lockup contract. The owner of this NFT can withdraw the streamed tokens, which are denominated in DAI.\\n\\n- Stream ID: 1\\n- Sablier Lockup Address: 0x923b5ab3714fd343316af5a5434582fd16722523\\n- DAI Address: 0xf62849f9a0b5bf2913b396098f7c7019b51a820a\\n\\n⚠️ WARNING: Transferring the NFT makes the new owner the recipient of the stream. The funds are not automatically withdrawn for the previous recipient.",
  "external_url": "https://sablier.com",
  "name": "Sablier Lockup #1",
  "image": "see image below"

Click to expand SVG preview

Click to preview description on Opensea

This NFT represents a stream in Sablier Lockup contract. The owner of this NFT can withdraw the streamed tokens, which are denominated in DAI.
    Stream ID: 1
    Sablier Lockup Address: 0x923b5ab3714fd343316af5a5434582fd16722523
    DAI Address: 0xf62849f9a0b5bf2913b396098f7c7019b51a820a
    ⚠️ WARNING: Transferring the NFT makes the new owner the recipient of the stream. The funds are not automatically withdrawn for the previous recipient.

[andreivladbrg]

good job, you were fast with this one

we can also remove these:

https://github.com/sablier-labs/v2-core/blob/9ef51a35fe0abe97fd5e4e6e93074f5212e37cf8/src/LockupNFTDescriptor.sol#L111-L116