build: don't pass --mode argument to V8 test-runner

V8's test-runner dropped the `--mode` argument some time back, and now
produces the following error if run with it:
  run-tests.py: error: no such option: --mode

PR-URL: #39055
Refs: #35705
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Makefile

@@ -665,12 +665,12 @@ test-v8: v8  ## Runs the V8 test suite on deps/v8.
 test-v8-intl: v8
 	export PATH="$(NO_BIN_OVERRIDE_PATH)" && \
 		deps/v8/tools/run-tests.py --gn --arch=$(V8_ARCH) \
-				--mode=$(BUILDTYPE_LOWER) intl \
+				intl \
 				$(TAP_V8_INTL)
 
 test-v8-benchmarks: v8
 	export PATH="$(NO_BIN_OVERRIDE_PATH)" && \
-		deps/v8/tools/run-tests.py --gn --arch=$(V8_ARCH) --mode=$(BUILDTYPE_LOWER) \
+		deps/v8/tools/run-tests.py --gn --arch=$(V8_ARCH) \
 				benchmarks \
 				$(TAP_V8_BENCHMARKS)