Revert "release_config: build flags can be lists"

Revert submission 2787001-product-build-flags

Reason for revert: Possible cause of b/308849337

Reverted changes: /q/submissionid:2787001-product-build-flags

Bug: 302593603
Bug: 308849337
Change-Id: I6246d20201e674ba99faf6b880ecdc7ef934c653

core/release_config.bzl

@@ -55,11 +55,6 @@ _all_flags_schema = {
             },
             "declared_in": {"type": "string"},
         },
-        "optional_keys": {
-            "appends": {
-                "type": "bool",
-            },
-        },
     },
 }
 
@@ -80,23 +75,17 @@ _all_values_schema = {
     },
 }
 
-def flag(name, partitions, default, _kwmarker = (), appends = False):
+def flag(name, partitions, default):
     """Declare a flag.
 
     Args:
       name: name of the flag
       partitions: the partitions where this should be recorded.
       default: the default value of the flag.
-      _kwmarker: Used to detect argument misuse.
-      appends: Whether new values should be append (not replace) the old.
 
     Returns:
       A dictionary containing the flag declaration.
     """
-
-    # If specified, appends must be a keyword value.
-    if _kwmarker != ():
-        fail("Too many positional parameters")
     if not partitions:
         fail("At least 1 partition is required")
     if not name.startswith("RELEASE_"):
@@ -116,7 +105,6 @@ def flag(name, partitions, default, _kwmarker = (), appends = False):
         "name": name,
         "partitions": partitions,
         "default": default,
-        "appends": appends,
     }
 
 def value(name, value):
@@ -165,12 +153,10 @@ def release_config(all_flags, all_values):
 
     # Validate flags
     flag_names = []
-    flags_dict = {}
     for flag in all_flags:
         if flag["name"] in flag_names:
             fail(flag["declared_in"] + ": Duplicate declaration of flag " + flag["name"])
         flag_names.append(flag["name"])
-        flags_dict[flag["name"]] = flag
 
     # Record which flags go on which partition
     partitions = {}
@@ -184,21 +170,13 @@ def release_config(all_flags, all_values):
             else:
                 partitions.setdefault(partition, []).append(flag["name"])
 
-    # Generate final values.
-    # Only declared flags may have a value.
+    # Validate values
+    # TODO(joeo): Disallow duplicate values after we've split AOSP and vendor flags.
     values = {}
     for value in all_values:
-        name = value["name"]
-        if name not in flag_names:
-            fail(value["set_in"] + ": Value set for undeclared build flag: " + name)
-        if flags_dict[name]["appends"]:
-            if name in values:
-                values[name]["value"] += " " + value["value"]
-                values[name]["set_in"] += " " + value["set_in"]
-            else:
-                values[name] = value
-        else:
-            values[name] = value
+        if value["name"] not in flag_names:
+            fail(value["set_in"] + ": Value set for undeclared build flag: " + value["name"])
+        values[value["name"]] = value
 
     # Collect values
     result = {