build-unit-test-docker: remove 'yamldir' option to phosphor-logging

phosphor-logging currently uses the `phosphor-dbus-interfaces.pc`
file by default to determine the location of the install YAML,
in order to generate appropriate headers for error metadata.
`phosphor-dbus-interfaces` changed where the YAML is installed, but
the yamldir value here did not match.  Remove it entirely and fall
back to obtaining the one from the pkg-config.

Tested: Ensured `phosphor-networkd` compiled using this container.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ibe2168a05e7ad5be0e497c9bcfc6cadac7607a5d
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index c7a9036..d6e2405 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -218,7 +218,6 @@
         config_flags=[
             "-Dlibonly=true",
             "-Dtests=disabled",
-            f"-Dyamldir={prefix}/share/phosphor-dbus-yaml/yaml",
         ],
     ),
     "openbmc/phosphor-objmgr": PackageDef(