Remove mb_config phases for codesearch builders.

These are no longer needed. The CS builder recipe is still passing in a phase
argument, but I'm removing that in a separate CL (crrev.com/c/1173943) which
I'll submit at the same time.

Bug: 833672
Change-Id: I9b273116cc8639116d01b124b7fe3749bda2a8f3
Reviewed-on: https://chromium-review.googlesource.com/1173941Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Joey Scarr <jsca@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583520}

tools/mb/mb_config.pyl

@@ -275,19 +275,10 @@
     },
 
     'chromium.infra.codesearch': {
-      'codesearch-gen-chromium-android': {
-        'android': 'codesearch_gen_chromium_android_bot',
-      },
-      'codesearch-gen-chromium-chromiumos': {
-        'chromeos': 'codesearch_gen_chromium_chromiumos_bot',
-        'linux': 'codesearch_gen_chromium_linux_bot',
-      },
-      'codesearch-gen-chromium-linux': {
-        'linux': 'codesearch_gen_chromium_linux_bot',
-      },
-      'codesearch-gen-chromium-win': {
-        'win': 'codesearch_gen_chromium_win_bot',
-      },
+      'codesearch-gen-chromium-android': 'codesearch_gen_chromium_android_bot',
+      'codesearch-gen-chromium-chromiumos': 'codesearch_gen_chromium_chromiumos_bot',
+      'codesearch-gen-chromium-linux': 'codesearch_gen_chromium_linux_bot',
+      'codesearch-gen-chromium-win': 'codesearch_gen_chromium_win_bot',
     },
 
     'chromium.linux': {