* New upstream release from the beta channel (FIREFOX_91_0b3_BUILD1)
* Drop obsolete patches
  - debian/patches/relax-cargo-dep.patch
* Update patches
  - debian/patches/armhf-reduce-linker-memory-use.patch
  - debian/patches/fix-armhf-webrtc-build.patch
  - debian/patches/rust-drop-dll-checksums.patch
  - debian/patches/ubuntu-ua-string-changes.patch
* Bump build-dep on rustc >= 1.51.0 and cargo >= 0.52
  - debian/control{,.in}