[M97][infra] Use python3 for all recipes.

This will ensure that new recipes that get added are run under python3.

(cherry picked from commit db1c9ea)

Change-Id: I632cb6b616807aa5448083320244551ab9540b58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3421266
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Garrett Beaty <gbeaty@google.com>
Cr-Original-Commit-Position: refs/heads/main@{#971936}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3469320
Auto-Submit: Garrett Beaty <gbeaty@google.com>
Commit-Queue: Stephen Martinis <martiniss@chromium.org>
Cr-Commit-Position: refs/branch-heads/4692@{#1519}
Cr-Branched-From: 038cd96-refs/heads/main@{#938553}

infra/config/recipes.star

@@ -12,7 +12,6 @@ def _recipe_for_package(cipd_package):
             name,
             cipd_version = None,
             recipe = None,
-            use_python3 = False,
             bootstrappable = False):
         """Declare a recipe for the given package.
 
@@ -27,7 +26,6 @@ def _recipe_for_package(cipd_package):
               information.
             cipd_version: See luci.recipe.
             recipe: See luci.recipe.
-            use_python3: See luci.recipe.
             bootstrappable: Whether or not the recipe supports the chromium
               bootstrapper. A recipe supports the bootstrapper if the following
               conditions are met:
@@ -59,7 +57,7 @@ def _recipe_for_package(cipd_package):
             cipd_version = cipd_version,
             recipe = recipe,
             use_bbagent = True,
-            use_python3 = use_python3,
+            use_python3 = True,
         )
 
         register_recipe_bootstrappability(name, bootstrappable)
@@ -98,7 +96,6 @@ build_recipe(
 
 build_recipe(
     name = "recipe:binary_size_trybot",
-    use_python3 = True,
 )
 
 build_recipe(
@@ -107,7 +104,6 @@ build_recipe(
 
 build_recipe(
     name = "recipe:binary_size_fuchsia_trybot",
-    use_python3 = True,
 )
 
 build_recipe(
@@ -121,19 +117,16 @@ build_recipe(
 build_recipe(
     name = "recipe:chromium",
     bootstrappable = True,
-    use_python3 = True,
 )
 
 build_recipe(
     name = "recipe:chromium/orchestrator",
     bootstrappable = True,
-    use_python3 = True,
 )
 
 build_recipe(
     name = "recipe:chromium/compilator",
     bootstrappable = True,
-    use_python3 = True,
 )
 
 build_recipe(
@@ -162,7 +155,6 @@ build_recipe(
 
 build_recipe(
     name = "recipe:chromium_libfuzzer_trybot",
-    use_python3 = True,
 )
 
 build_recipe(
@@ -172,7 +164,6 @@ build_recipe(
 build_recipe(
     name = "recipe:chromium_trybot",
     bootstrappable = True,
-    use_python3 = True,
 )
 
 build_recipe(
@@ -202,7 +193,6 @@ build_recipe(
 
 build_recipe(
     name = "recipe:presubmit",
-    use_python3 = True,
 )
 
 build_recipe(