mb: Remove a redundant mixin

no_pch and disable_precompiled_headers do the same thing; drop one of them.

No behavior change.

BUG=none

Review-Url: https://codereview.chromium.org/2148953002
Cr-Commit-Position: refs/heads/master@{#405245}

tools/mb/mb_config.pyl

@@ -1203,8 +1203,7 @@
     ],
 
     'gn_windows_analyze': [
-      'gn', 'no_symbols', 'disable_precompiled_headers',
-      'shared', 'x86', 'win_analyze',
+      'gn', 'no_symbols', 'no_pch', 'shared', 'x86', 'win_analyze',
     ],
 
     'gn_ubsan_vptr_release_bot': [
@@ -2025,11 +2024,6 @@
       'gyp_defines': 'disable_nacl=1',
     },
 
-    'disable_precompiled_headers': {
-      'gn_args': 'disable_precompiled_headers=true',
-      'gyp_defines': 'chromium_win_pch=0',
-    },
-
     'edge': {
       'gn_args': 'sanitizer_coverage_flags="edge"',
       'gyp_defines': 'sanitizer_coverage=edge',