test: Makefile.am: Remove -lstdc++fs

56d14d04 dropped experimental::filesystem and removed one
-lstdc++fs, this removes the other.

Tested: Built the repo.
Change-Id: I085ad483b317b0018e45001d6d12740ec662d811
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
1 file changed