Move unit tests to the location Meson expects them to be

Everything that is a separate subproject should live in the subprojects
directory.

Progress on #2503

This reverts commit 451f8a8c19.

src/libstore-tests/uds-remote-store.cc

@@ -0,0 +1,23 @@
+// FIXME: Odd failures for templates that are causing the PR to break
+// for now with discussion with @Ericson2314 to comment out.
+#if 0
+#  include <gtest/gtest.h>
+
+#  include "uds-remote-store.hh"
+
+namespace nix {
+
+TEST(UDSRemoteStore, constructConfig)
+{
+    UDSRemoteStoreConfig config{"unix", "/tmp/socket", {}};
+
+    EXPECT_EQ(config.path, "/tmp/socket");
+}
+
+TEST(UDSRemoteStore, constructConfigWrongScheme)
+{
+    EXPECT_THROW(UDSRemoteStoreConfig("http", "/tmp/socket", {}), UsageError);
+}
+
+} // namespace nix
+#endif