Auto merge of #15099 - servo:phf-no-macros, r=jdm

Remove usage of phf_macros.

It’s a compiler plugin that uses unstable compiler APIs that are not on a path to stabilization.

With this changes, there is one less thing that might break when we update the compiler. For example: https://github.com/sfackler/rust-phf/pull/101

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/15099)
<!-- Reviewable:end -->

ports/servo/Cargo.toml

@@ -41,7 +41,6 @@ browserhtml = {git = "https://github.com/browserhtml/browserhtml", branch = "cra
 glutin_app = {path = "../../ports/glutin"}
 log = "0.3"
 libservo = {path = "../../components/servo"}
-phf_macros = "0.7.19"
 
 [target.'cfg(not(target_os = "android"))'.dependencies]
 sig = "0.1"