selftests: net: move EXTRA_CLEAN of libynl.a into ynl.mk

Commit 1fd9e4f ("selftests: make kselftest-clean remove libynl outputs")
added EXTRA_CLEAN of YNL generated files to ynl.mk. We already had
a EXTRA_CLEAN in the file including the snippet. Consolidate them.

Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20241011230311.2529760-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/Makefile

@@ -98,7 +98,6 @@ TEST_PROGS += vlan_hw_filter.sh
 TEST_PROGS += bpf_offload.py
 
 # YNL files, must be before "include ..lib.mk"
-EXTRA_CLEAN += $(OUTPUT)/libynl.a
 YNL_GEN_FILES := ncdevmem
 TEST_GEN_FILES += $(YNL_GEN_FILES)
 

tools/testing/selftests/net/ynl.mk

@@ -33,4 +33,5 @@ $(OUTPUT)/libynl.a: $(YNL_SPECS) $(OUTPUT)/.libynl-$(YNL_GENS_HASH).sig
 EXTRA_CLEAN += \
 	$(top_srcdir)/tools/net/ynl/lib/__pycache__ \
 	$(top_srcdir)/tools/net/ynl/lib/*.[ado] \
-	$(OUTPUT)/.libynl-*.sig
+	$(OUTPUT)/.libynl-*.sig \
+	$(OUTPUT)/libynl.a