Remove redundant begin block

We enabled `Style/RedundantBegin` cop at #34764, but it is hard to
detect an offence if returning value put after the block.

activerecord/lib/active_record/middleware/database_selector/resolver.rb

@@ -64,13 +64,10 @@ def read_from_replica(&blk)
           def write_to_primary(&blk)
             ActiveRecord::Base.connected_to(role: :writing) do
               instrumenter.instrument("database_selector.active_record.wrote_to_primary") do
-                begin
-                  ret = yield
+                yield
               ensure
                 resolver.update_last_write_timestamp
               end
-                ret
-              end
             end
           end