mail-parser: Remove invalid requirements.txt patch

[polygon]

Upstream modified requirements.txt and is no longer pinning
dependencies to exact versions. Instead, it provides version
bounds. Also, the ipaddress dependency is now limited already
in requirements.txt to Python versions < 3.3.

Removed all the patching since it generated an invalid
requirements.txt that caused the build to fail.

Motivation for this change

Build fails since updating from 3.12.0 to 3.15.0. Patching from Nix-derivation would create an invalid requirements.txt after upstream changes to that file.

ZHF: #122042

@jonringer

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[r-rmcgibbo]

Result of nixpkgs-review pr 122875 at 652e738 run on aarch64-linux 1

2 packages built successfully:

• python38Packages.mail-parser
• python39Packages.mail-parser

---

Result of nixpkgs-review pr 122875 at 652e738 run on x86_64-linux 1

2 packages built successfully:

• python38Packages.mail-parser
• python39Packages.mail-parser

[risicle]

WFM macos 10.15 & nixos x86_64