Clarify target removal approvals for different Target Tiers

Author: jieyouxu

src/compiler/proposals-and-stabilization.md

@@ -285,14 +285,25 @@ circumstance.
   - Open an RFC describing the motivation for the change and start an FCP to approve, start an FCP.
   - If approved, the change should be accompanied by a blog post announcing the change with a
     notice period of at least one release before the change applies.
-- Demoting/removing a target
+- Demoting/removing a Tier 1 target
+  - **Propose using:** RFC
+  - **Approve using:** FCP
+  - Demoting a Tier 1 target requires a RFC as per the
+    [Tier 1 Target Policy][tier-1-target-policy]. Consult the
+    [Tier 1 Target Policy][tier-1-target-policy] for approval and community
+    communication requirements.
+- Demoting/removing a Tier 2 target
   - **Propose using:** MCP
   - **Approve using:** FCP
-  - Write an MCP describing why the target should be demoted/removed and once discussion has
+  - Write an MCP describing why the Tier 2 target should be demoted/removed and once discussion has
     concluded, an FCP can be started to approve the demotion/removal.
-  - If approved and affecting a tier 2 or tier 1 target, the change should be accompanied by a
-    blog post announcing the change with a notice period of at least one release before the change
-    applies.
+  - If approved, the change should be accompanied by a blog post announcing the change with a
+    notice period of at least one release before the change applies.
+- Removing a Tier 3 target
+  - **Propose using:** PR
+  - **Approve using:** r+ (compiler leads)
+  - Open an PR with the proposed removal and describe the motivation, and obtain a r+ from a
+    compiler team lead.
 - Changing target baseline (e.g. minimum Darwin or Windows version bump)
   - **Propose using:** MCP
   - **Approve using:** FCP
@@ -376,3 +387,4 @@ See [*Adding ecosystem/integration test jobs/components to rust-lang/rust CI*](.
 [compiler_lint_eg]: https://doc.rust-lang.org/rustc/lints/listing/deny-by-default.html#explicit-builtin-cfgs-in-flags
 [ecosystem_testing]: https://rustc-dev-guide.rust-lang.org/tests/ecosystem.html
 [compiler-fcp]: https://github.com/rust-lang/team/blob/master/teams/compiler-fcp.toml
+[tier-1-target-policy]: https://doc.rust-lang.org/rustc/target-tier-policy.html#tier-1-target-policy