revert: leave expression/json_serde.cc untouched (out of PR scope)

Revert the float/double LiteralFromJson leniency change and its test: that is the
pre-existing shared literal parser, not code this PR introduces. The integer-encoded
float-default interop gap (Java writes float defaults as bare ints) is a separate
follow-up in a PR that owns the expression serde.

Author: huan233usc

src/iceberg/expression/json_serde.cc

@@ -342,15 +342,13 @@ Result<Literal> LiteralFromJson(const nlohmann::json& json, const Type* type) {
       return Literal::Long(json.get<int64_t>());
 
     case TypeId::kFloat:
-      // Accept an integer JSON token too (e.g. `1`), matching Java's lenient numeric
-      // parsing; otherwise a float default written as a bare integer fails to read.
-      if (!json.is_number()) [[unlikely]] {
+      if (!json.is_number_float()) [[unlikely]] {
         return JsonParseError("Cannot parse {} as a float value", SafeDumpJson(json));
       }
       return Literal::Float(json.get<float>());
 
     case TypeId::kDouble:
-      if (!json.is_number()) [[unlikely]] {
+      if (!json.is_number_float()) [[unlikely]] {
         return JsonParseError("Cannot parse {} as a double value", SafeDumpJson(json));
       }
       return Literal::Double(json.get<double>());

src/iceberg/test/schema_json_test.cc

@@ -258,17 +258,6 @@ TEST(SchemaJsonTest, CrossTypeDefaultNormalizedRoundTrip) {
   EXPECT_EQ(original, *reparsed);
 }
 
-TEST(SchemaJsonTest, FloatDefaultAcceptsIntegerEncoding) {
-  // Java writes a float/double default as a bare integer token (e.g. 1, not 1.0); it must
-  // parse, matching Java's lenient numeric reading.
-  constexpr std::string_view json =
-      R"({"fields":[{"id":1,"initial-default":1,"name":"f","required":true,"type":"float"}],"schema-id":1,"type":"struct"})";
-  ICEBERG_UNWRAP_OR_FAIL(auto schema, SchemaFromJson(nlohmann::json::parse(json)));
-  const auto& field = schema->fields()[0];
-  ASSERT_NE(field.initial_default(), nullptr);
-  EXPECT_EQ(*field.initial_default(), Literal::Float(1.0F));
-}
-
 TEST(SchemaJsonTest, UnknownFieldRoundTrip) {
   constexpr std::string_view json =
       R"({"fields":[{"id":1,"name":"mystery","required":false,"type":"unknown"}],"schema-id":1,"type":"struct"})";