Remove android_clang_dbg from PRESUBMIT.py

This bot is no longer in CQ and is subsumed by
android_clang_dbg_recipe.  It is a waste of resources to run two bots
by default.

Also, we are bringing up a replacement for android_clang_dbg_recipe
(see the linked bug), and this would allow us to recycle the shorter
bot name.

R=phajdan.jr@chromium.org
BUG=434516
TEST=git cl try: doesn't trigger android_clang_dbg

Review URL: https://codereview.chromium.org/751613004

Cr-Commit-Position: refs/heads/master@{#305460}

PRESUBMIT.py

@@ -1598,7 +1598,6 @@ def GetDefaultTryConfigs(bots=None):
       'android_arm64_dbg_recipe': ['slave_steps'],
       'android_chromium_gn_compile_dbg': ['compile'],
       'android_chromium_gn_compile_rel': ['compile'],
-      'android_clang_dbg': ['slave_steps'],
       'android_clang_dbg_recipe': ['slave_steps'],
       'android_dbg_tests_recipe': ['slave_steps'],
       'cros_x86': ['defaulttests'],
@@ -1699,7 +1698,6 @@ def GetPreferredTryMasters(project, change):
   if all(re.search(r'(^|[\\\/_])android[\\\/_.]', f) for f in files):
     return GetDefaultTryConfigs([
         'android_aosp',
-        'android_clang_dbg',
         'android_dbg_tests_recipe',
     ])
   if all(re.search(r'[\\\/_]ios[\\\/_.]', f) for f in files):
@@ -1709,7 +1707,6 @@ def GetPreferredTryMasters(project, change):
       'android_arm64_dbg_recipe',
       'android_chromium_gn_compile_rel',
       'android_chromium_gn_compile_dbg',
-      'android_clang_dbg',
       'android_clang_dbg_recipe',
       'android_dbg_tests_recipe',
       'ios_dbg_simulator',