Bug 1421097 - Require at least Rust 1.22.1. r=ted

Bump the minimum required Rust version now that 1.22.1
has been in stable release for more than two weeks.

Version 1.22.0 works fine everywhere but macOS 10.13,
but 1.22.1 was released the same day, so it's no harder
to upgrade to.

Also update the base-toolchain builds to ensure we
continue to build with this version.

MozReview-Commit-ID: GlRWUNE07G0

--HG--
extra : rebase_source : f37585db5633e6e64b02bc94c2516b5ab18c3e15

build/moz.configure/rust.configure

@@ -66,7 +66,7 @@ def rust_compiler(rustc_info, cargo_info):
         You can install rust by running './mach bootstrap'
         or by directly running the installer from https://rustup.rs/
         '''))
-    rustc_min_version = Version('1.21.0')
+    rustc_min_version = Version('1.22.1')
     cargo_min_version = Version('0.{}'.format(rustc_min_version.minor + 1))
 
     version = rustc_info.version

taskcluster/ci/build/linux.yml

@@ -218,7 +218,7 @@ linux64-base-toolchains/opt:
     toolchains:
         - linux64-clang-3.9
         - linux64-gcc-4.9
-        - linux64-rust-1.21
+        - linux64-rust-1.22
         - linux64-sccache
 
 linux64-base-toolchains/debug:
@@ -250,7 +250,7 @@ linux64-base-toolchains/debug:
     toolchains:
         - linux64-clang-3.9
         - linux64-gcc-4.9
-        - linux64-rust-1.21
+        - linux64-rust-1.22
         - linux64-sccache
 
 linux/opt:

taskcluster/ci/toolchain/linux.yml

@@ -346,30 +346,6 @@ linux64-rust-1.22:
         toolchain-alias: linux64-rust
         toolchain-artifact: public/build/rustc.tar.xz
 
-linux64-rust-1.21:
-    description: "rust repack"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(rust-1.21)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux
-    worker:
-        docker-image: {in-tree: desktop-build}
-        max-run-time: 7200
-        env:
-            UPLOAD_DIR: artifacts
-    run:
-        using: toolchain-script
-        script: repack_rust.py
-        arguments: [
-            '--channel', '1.21.0',
-            '--host', 'x86_64-unknown-linux-gnu',
-            '--target', 'x86_64-unknown-linux-gnu',
-            '--target', 'i686-unknown-linux-gnu',
-        ]
-        toolchain-artifact: public/build/rustc.tar.xz
-
 linux64-rust-1.19:
     description: "rust repack"
     treeherder: