Revert "testing: Ignore unknown memory in leak detective"

This reverts commit b998695344.

Seems like this is not necessary anymore.  Possibly because of
8ff3238027 ("openssl: Prevent OpenSSL from using posix_memalign() if
LD is enabled").

testing/hosts/default/etc/ssh/sshd_config

@@ -13,5 +13,4 @@ PrintLastLog no
 UsePAM no
 AcceptEnv LANG LC_*
 AcceptEnv LEAK_DETECTIVE_*
-SetEnv LEAK_DETECTIVE_IGNORE_UNKNOWN=1
 Subsystem	sftp	/usr/lib/openssh/sftp-server

testing/hosts/default/etc/systemd/system.conf.d/99-ignore-unknown-memory.conf

@@ -1,2 +0,0 @@
-[Manager]
-DefaultEnvironment=LEAK_DETECTIVE_IGNORE_UNKNOWN=1