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.

tests/unit/libstore-support/tests/path.cc

@@ -1,80 +0,0 @@
-#include <rapidcheck/gen/Arbitrary.h>
-#include <regex>
-
-#include <rapidcheck.h>
-
-#include "path-regex.hh"
-#include "store-api.hh"
-
-#include "tests/hash.hh"
-#include "tests/path.hh"
-
-namespace nix {
-
-void showValue(const StorePath & p, std::ostream & os)
-{
-    os << p.to_string();
-}
-
-}
-
-namespace rc {
-using namespace nix;
-
-Gen<char> storePathChar()
-{
-    return rc::gen::apply([](uint8_t i) -> char {
-        switch (i) {
-            case 0 ... 9:
-                return '0' + i;
-            case 10 ... 35:
-                return 'A' + (i - 10);
-            case 36 ... 61:
-                return 'a' + (i - 36);
-            case 62:
-                return '+';
-            case 63:
-                return '-';
-            case 64:
-                return '.';
-            case 65:
-                return '_';
-            case 66:
-                return '?';
-            case 67:
-                return '=';
-            default:
-                assert(false);
-        }
-    },
-    gen::inRange<uint8_t>(0, 10 + 2 * 26 + 6));
-}
-
-Gen<StorePathName> Arbitrary<StorePathName>::arbitrary()
-{
-    return gen::construct<StorePathName>(
-        gen::suchThat(
-            gen::container<std::string>(storePathChar()),
-            [](const std::string & s) {
-                return
-                    !( s == ""
-                    || s == "."
-                    || s == ".."
-                    || s.starts_with(".-")
-                    || s.starts_with("..-")
-                    );
-            }
-        )
-    );
-}
-
-Gen<StorePath> Arbitrary<StorePath>::arbitrary()
-{
-    return
-        gen::construct<StorePath>(
-            gen::arbitrary<Hash>(),
-            gen::apply([](StorePathName n){ return n.name; }, gen::arbitrary<StorePathName>())
-        );
-}
-
-} // namespace rc