cleanup goma_client_json support

goma_client_json is no longer supported.

BUG=chromium:1359171
TEST=./run_tests

Change-Id: Ic3ba2f341fa7e026b22b2cfc410fa2287658e516
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4160820
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Madeleine Hardt <hardtmad@google.com>
Tested-by: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Junji Watanabe <jwata@google.com>
diff --git a/scripts/build_packages.py b/scripts/build_packages.py
index d8af3bd..20b156f 100644
--- a/scripts/build_packages.py
+++ b/scripts/build_packages.py
@@ -375,8 +375,7 @@
     # This option; 1) starts goma, 2) builds packages (expecting that goma is
     # used), then 3) stops goma explicitly.
     # 4) is a request from the goma team, so that stats/logs can be taken.
-    # Note: GOMA_DIR and GOMA_SERVICE_ACCOUNT_JSON_FILE are expected to be passed
-    # via env var.
+    # Note: GOMA_DIR is expected to be passed via env var.
     #
     # In local dev env cases, compiler_proxy is expected to keep running.
     # In such a case;