Require scl files in ExecutionModeScl

Also remove json from scl file builtins, as it's not in bazel.

Bug: 309686282
Test: Presubmits
Change-Id: I6227c5dc14922b4682380254b4716b4ae38c47b9
diff --git a/tools/rbcrun/host_test.go b/tools/rbcrun/host_test.go
index 7cfeb14..38b2923 100644
--- a/tools/rbcrun/host_test.go
+++ b/tools/rbcrun/host_test.go
@@ -143,7 +143,7 @@
 	if err := os.Chdir(filepath.Dir(dir)); err != nil {
 		t.Fatal(err)
 	}
-	vars, _, err := Run("testdata/bzl_loads_scl.bzl", nil, ExecutionModeScl, false)
+	vars, _, err := Run("testdata/bzl_loads_scl.bzl", nil, ExecutionModeRbc, false)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -160,7 +160,7 @@
 	if err := os.Chdir(filepath.Dir(dir)); err != nil {
 		t.Fatal(err)
 	}
-	vars, _, err := Run("testdata/bzl_loads_scl_2.bzl", nil, ExecutionModeScl, false)
+	vars, _, err := Run("testdata/bzl_loads_scl_2.bzl", nil, ExecutionModeRbc, false)
 	if err != nil {
 		t.Fatal(err)
 	}