modules: Drop the .export_symbol section from the final modules

[ Upstream commit 8fe51b45 ]

Commit ddb5cdba ("kbuild: generate KSYMTAB entries by modpost")
forget drop the .export_symbol section from the final modules.

Fixes: ddb5cdba ("kbuild: generate KSYMTAB entries by modpost")
Signed-off-by: Wang Yao <wangyao@lemote.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>