Stop retrying semaphore decrement when getting a deadlock

This was added in d72fe46 and initially,
it seemed like a good idea, but it ended up causing a different error
as it messed with Active Record's transactions. The error would be
```
ActiveRecord::StatementInvalid (Mysql2::Error: SAVEPOINT active_record_1 does not exist)
```
And this made us realise it might be more complicated, because we might be
in a transaction that wraps the Solid Queue transaction.

Since this is such an edge case that happens only with certain job loads
and perhaps only with MySQL, InnoDB and READ COMMITTED, let's stop trying to
be too clever about it, and instead, simplify this a bit by avoiding the
decrement at all when the semaphore's limit is 1 and it was just created.

Author: rosa

app/models/solid_queue/semaphore.rb

@@ -26,7 +26,6 @@ def self.signal_all(jobs)
 
       def initialize(job)
         @job = job
-        @retries = 0
       end
 
       def wait
@@ -42,42 +41,26 @@ def signal
       end
 
       private
-        attr_accessor :job, :retries
+        attr_accessor :job
 
         def attempt_creation
           Semaphore.create!(key: key, value: limit - 1, expires_at: expires_at)
           true
         rescue ActiveRecord::RecordNotUnique
-          attempt_decrement
+          if limit == 1 then false
+          else
+            attempt_decrement
+          end
         end
 
         def attempt_decrement
           Semaphore.available.where(key: key).update_all([ "value = value - 1, expires_at = ?", expires_at ]) > 0
-        rescue ActiveRecord::Deadlocked
-          if retriable? then attempt_retry
-          else
-            raise
-          end
         end
 
         def attempt_increment
           Semaphore.where(key: key, value: ...limit).update_all([ "value = value + 1, expires_at = ?", expires_at ]) > 0
         end
 
-        def attempt_retry
-          self.retries += 1
-
-          if semaphore = Semaphore.find_by(key: key)
-            semaphore.value > 0 && attempt_decrement
-          end
-        end
-
-        MAX_RETRIES = 1
-
-        def retriable?
-          retries < MAX_RETRIES
-        end
-
         def key
           job.concurrency_key
         end