selftest/lkdtm: Use local .gitignore

Commit 68ca0fd272 ("selftest/lkdtm: Don't pollute 'git status'")
introduced patterns for git to ignore files generated in
tools/testing/selftests/lkdtm/

Use local .gitignore file instead of using the root one.

Fixes: 68ca0fd272 ("selftest/lkdtm: Don't pollute 'git status'")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

.gitignore

@@ -100,10 +100,6 @@ modules.order
 /include/ksym/
 /arch/*/include/generated/
 
-# Generated lkdtm tests
-/tools/testing/selftests/lkdtm/*.sh
-!/tools/testing/selftests/lkdtm/run.sh
-
 # stgit generated dirs
 patches-*