Revert "[infra] Flutter bot should sync to origin/skia-master"

This reverts commit 8061053b73e217b648d33e0da09d9cb3725b6ae3.

Reason for revert: skia-master branch no longer exists

Original change's description:
> [infra] Flutter bot should sync to origin/skia-master
> 
> Bug: skia:
> Change-Id: I223bef522ff8605674f4ecabcbd0624cfc92cb06
> Reviewed-on: https://skia-review.googlesource.com/c/173224
> Reviewed-by: Ravi Mistry <rmistry@google.com>
> Commit-Queue: Eric Boren <borenet@google.com>

TBR=borenet@google.com,rmistry@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: skia:
Change-Id: I3a40a0c6f4a354650d354f2eb4f9d20defe70a0a
Reviewed-on: https://skia-review.googlesource.com/c/178023
Reviewed-by: Ravi Mistry <rmistry@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
diff --git a/infra/bots/recipe_modules/checkout/api.py b/infra/bots/recipe_modules/checkout/api.py
index 3c4ed76..cc91492 100644
--- a/infra/bots/recipe_modules/checkout/api.py
+++ b/infra/bots/recipe_modules/checkout/api.py
@@ -94,7 +94,7 @@
     if checkout_flutter:
       # Skia is a DEP of Flutter; the 'revision' property is a Skia revision,
       # and any patch should be applied to Skia, not Flutter.
-      main.revision = 'origin/skia-master'
+      main.revision = 'origin/master'
       main.managed = True
       m[main_name] = 'got_flutter_revision'
       if flutter_android:
diff --git a/infra/bots/recipe_modules/checkout/examples/full.expected/flutter_trybot.json b/infra/bots/recipe_modules/checkout/examples/full.expected/flutter_trybot.json
index 1263543..da67b7a 100644
--- a/infra/bots/recipe_modules/checkout/examples/full.expected/flutter_trybot.json
+++ b/infra/bots/recipe_modules/checkout/examples/full.expected/flutter_trybot.json
@@ -47,7 +47,7 @@
       "--patch_ref",
       "https://skia.googlesource.com/skia.git@refs/changes/89/456789/12",
       "--revision",
-      "src/flutter@origin/skia-master",
+      "src/flutter@origin/master",
       "--revision",
       "src/third_party/skia@abc123"
     ],
@@ -64,7 +64,7 @@
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"did_run\": true, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"fixed_revisions\": {@@@",
-      "@@@STEP_LOG_LINE@json.output@    \"src/flutter\": \"origin/skia-master\", @@@",
+      "@@@STEP_LOG_LINE@json.output@    \"src/flutter\": \"origin/master\", @@@",
       "@@@STEP_LOG_LINE@json.output@    \"src/third_party/skia\": \"abc123\"@@@",
       "@@@STEP_LOG_LINE@json.output@  }, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"manifest\": {@@@",
diff --git a/infra/bots/recipes/compile.expected/Build-Debian9-GCC-x86_64-Release-Flutter_Android.json b/infra/bots/recipes/compile.expected/Build-Debian9-GCC-x86_64-Release-Flutter_Android.json
index befcc93..1046f27 100644
--- a/infra/bots/recipes/compile.expected/Build-Debian9-GCC-x86_64-Release-Flutter_Android.json
+++ b/infra/bots/recipes/compile.expected/Build-Debian9-GCC-x86_64-Release-Flutter_Android.json
@@ -45,7 +45,7 @@
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
-      "src/flutter@origin/skia-master",
+      "src/flutter@origin/master",
       "--revision",
       "src/third_party/skia@abc123"
     ],
@@ -62,7 +62,7 @@
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"did_run\": true, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"fixed_revisions\": {@@@",
-      "@@@STEP_LOG_LINE@json.output@    \"src/flutter\": \"origin/skia-master\", @@@",
+      "@@@STEP_LOG_LINE@json.output@    \"src/flutter\": \"origin/master\", @@@",
       "@@@STEP_LOG_LINE@json.output@    \"src/third_party/skia\": \"abc123\"@@@",
       "@@@STEP_LOG_LINE@json.output@  }, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"manifest\": {@@@",