rust: kbuild: remove skipping of -Wrustdoc::unescaped_backticks

Back in Rust 1.82.0, I cleaned the `rustdoc::unescaped_backticks` lint in
upstream Rust and added tests so that hopefully it would not regress [1].

Thus we can remove it from our side given the Rust minimum version bump.

Link: https://github.com/rust-lang/rust/pull/128307 [1]
Reviewed-by: Tamir Duberstein <tamird@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260405235309.418950-12-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/Makefile

@@ -75,8 +75,7 @@ core-edition := $(if $(call rustc-min-version,108700),2024,2021)
 
 core-skip_flags := \
     --edition=2021 \
-    -Wunreachable_pub \
-    -Wrustdoc::unescaped_backticks
+    -Wunreachable_pub
 
 core-flags := \
     --edition=$(core-edition) \
@@ -209,8 +208,6 @@ rustdoc-macros: $(src)/macros/lib.rs rustdoc-clean rustdoc-proc_macro2 \
     rustdoc-quote rustdoc-syn FORCE
 	+$(call if_changed,rustdoc)
 
-# Starting with Rust 1.82.0, skipping `-Wrustdoc::unescaped_backticks` should
-# not be needed -- see https://github.com/rust-lang/rust/pull/128307.
 rustdoc-core: private skip_flags = $(core-skip_flags)
 rustdoc-core: private rustc_target_flags = $(core-flags)
 rustdoc-core: $(RUST_LIB_SRC)/core/src/lib.rs rustdoc-clean FORCE