test(codegen): generalize ceiling failure message

The message renders for any fixture in the ceilings list, which spans
all five protocols, but it named the JSON protocol's per-operation
error-code mapper as an expected lambda. That was misleading when a
query or xml fixture is the one that regressed, and it also placed
the mapper under expected per-client lambdas when the mapper is
per-operation. Drop the sentence; the actionable half of it, to hoist
a per-operation construct into a shared helper, is kept.

Correct the cost of one per-operation lambda from ~6 pool entries per
operation to roughly 5, which is the measured figure.

Author: zoewangg

codegen/src/test/java/software/amazon/awssdk/codegen/poet/client/ClientLambdaCallSiteCeilingTest.java

@@ -78,12 +78,10 @@ private static String regressionMessage(String fixture, int callSites, int ceili
         return String.format(
             Locale.ROOT,
             "%s contains %d lambda call sites, ceiling is %d.%n%n"
-            + "Per-operation lambdas are the dominant removable constant pool cost in generated clients: one per "
-            + "operation costs ~6 pool entries per operation. This fixture has %d operations, so a lambda added to "
-            + "every operation body raises this count by %d.%n%n"
-            + "Expected per-client lambdas are shared helpers (metric publishing) and the per-operation error-code "
-            + "mapper that the JSON protocol requires. If you added a construct to every operation body, hoist it into "
-            + "a shared helper.%n%n"
+            + "Per-operation lambdas are the dominant removable constant pool cost in generated clients: each one costs "
+            + "roughly 5 pool entries per operation. This fixture has %d operations, so a lambda added to every "
+            + "operation body raises this count by %d.%n%n"
+            + "If you added a construct to every operation body, hoist it into a shared helper.%n%n"
             + "If the growth is intended and justified, raise the ceiling deliberately and record the reason "
             + "alongside it.",
             fixture, callSites, ceiling, operations, operations);