btf, scripts: rust: drop is_rust_module.sh

With commit c117797 ("btf, scripts: Exclude Rust CUs with pahole")
we are now able to use pahole directly to identify Rust compilation
units (CUs) and exclude them from generating BTF debugging information
(when DEBUG_INFO_BTF is enabled).

And if pahole doesn't support the --lang-exclude flag, we can't enable
both RUST and DEBUG_INFO_BTF at the same time.

So, in any case, the script is_rust_module.sh is just redundant and we
can drop it.

NOTE: we may also be able to drop the "Rust loadable module" mark
inside Rust modules, but it seems safer to keep it for now to make sure
we are not breaking any external tool that may potentially rely on it.

Signed-off-by: Andrea Righi <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Tested-by: Eric Curtin <[email protected]>
Reviewed-by: Eric Curtin <[email protected]>
Reviewed-by: Neal Gompa <[email protected]>
Reviewed-by: Masahiro Yamada <[email protected]>
Reviewed-by: Martin Rodriguez Reboredo <[email protected]>
Acked-by: Daniel Xu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Picked the `Reviewed-by`s from the old patch too. ]
Signed-off-by: Miguel Ojeda <[email protected]>

Author: Andrea Righi

rust/macros/module.rs

@@ -199,7 +199,7 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream {
             /// Used by the printing macros, e.g. [`info!`].
             const __LOG_PREFIX: &[u8] = b\"{name}\\0\";
 
-            /// The \"Rust loadable module\" mark, for `scripts/is_rust_module.sh`.
+            /// The \"Rust loadable module\" mark.
             //
             // This may be best done another way later on, e.g. as a new modinfo
             // key or a new section. For the moment, keep it simple.

scripts/Makefile.modfinal

@@ -41,8 +41,6 @@ quiet_cmd_btf_ko = BTF [M] $@
       cmd_btf_ko = 							\
 	if [ ! -f vmlinux ]; then					\
 		printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \
-	elif [ -n "$(CONFIG_RUST)" ] && $(srctree)/scripts/is_rust_module.sh $@; then 		\
-		printf "Skipping BTF generation for %s because it's a Rust module\n" $@ 1>&2; \
 	else								\
 		LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J $(PAHOLE_FLAGS) --btf_base vmlinux $@; \
 		$(RESOLVE_BTFIDS) -b vmlinux $@; 			\