presubmit_support: remove backslash from log

This removes backslash from log like
```
Python 2 scripts were run during Python 2 presubmits. Please see https://bugs.chromium.org/p/chromium/issues/detail?id=1313804#c61 for tips on resolving this.
  scripts/common/env.py print from /usr/local/google/home/tikuta/chrome_infra/build \
  /usr/local/google/home/tikuta/chrome_infra/build/recipes/unittests/recipe_test.py from /usr/local/google/home/tikuta/chrome_infra/build \
  -u /usr/local/google/home/tikuta/chrome_infra/build/recipes/.recipe_deps/recipe_engine/recipe_engine/main.py --package /usr/local/google/home/tikuta/chrome_infra/build/infra/config/recipes.cfg test run from /usr/local/google/home/tikuta/chrome_infra/build \
  -u /usr/local/google/home/tikuta/chrome_infra/build/recipes/.recipe_deps/recipe_engine/recipe_engine/main.py --package /usr/local/google/home/tikuta/chrome_infra/build/infra/config/recipes.cfg --proto-override /usr/local/google/home/tikuta/chrome_infra/build/recipes/.recipe_deps/_pb --log-level ERROR -O depot_too
ls=/usr/local/google/home/tikuta/chrome_infra/build/recipes/.recipe_deps/depot_tools -O chromiumos_proto=/usr/local/google/home/tikuta/chrome_infra/build/recipes/.recipe_deps/chromiumos_proto -O infra=/usr/local/google/home/tikuta/chrome_infra/build/recipes/.recipe_deps/infra -O recipe_engine=/usr/local/google/home
/tikuta/chrome_infra/build/recipes/.recipe_deps/recipe_engine -O chromeos=/usr/local/google/home/tikuta/chrome_infra/build/recipes/.recipe_deps/chromeos -O chromiumos_config=/usr/local/google/home/tikuta/chrome_infra/build/recipes/.recipe_deps/chromiumos_config test _runner --cov-file /tmp/tmpqNhYvj.recipe_test_cov
erage/thread-0.coverage --cover-module-imports from /usr/local/google/home/tikuta/chrome_infra/build \
```

I think this backslash is bit confusing there.

Change-Id: If5911e27808cfcde029d5ea2b34dda06847085ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3827922
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>

presubmit_support.py

@@ -366,12 +366,10 @@ class _PresubmitResult(object):
   def handle(self):
     sys.stdout.write(self._message)
     sys.stdout.write('\n')
-    for index, item in enumerate(self._items):
+    for item in self._items:
       sys.stdout.write('  ')
       # Write separately in case it's unicode.
       sys.stdout.write(str(item))
-      if index < len(self._items) - 1:
-        sys.stdout.write(' \\')
       sys.stdout.write('\n')
     if self._long_text:
       sys.stdout.write('\n***************\n')