Fix Score V1 simulation in scoring test scene incorrectly applying multiplier

`TestSceneScoring` included a local simulation of stable's Score V1
algorithm. One of the parts of said algorithm is a mysterious
"score multiplier", influenced by - among others - the beatmap's drain
rate, overall difficulty, circle size, object count, drain length,
and active mods. (An implementation of this already exists in lazer
source, in `OsuLegacyScoreSimulator`, but more on this later.)

However, `TestSceneScoring` had this multiplier in _two_ places, with
_two_ distinct values, one of which being 1 (i.e. basically off).
Unfortunately, the place that had 1 as the multiplier was the wrong one.

Stable calculates the score increase for every hit in two stages;
first, it takes the raw numerical value of the judgement, but then
applies a combo-based bonus on top of it:

    scoreIncrease += (int)(Math.Max(0, ComboCounter.HitCombo - 1) * (scoreIncrease / 25 * ScoreMultiplier));

On the face of it, it may appear that the `ScoreMultiplier` factor
can be factored out and applied at the end only when returning total
score. However, once the above formula is rewritten as:

    scoreIncrease = scoreIncrease + (int)(Math.Max(0, ComboCounter.HitCombo - 1) * (scoreIncrease / 25 * ScoreMultiplier));
                  = scoreIncrease * (1 + (Math.Max(0, ComboCounter.HitCombo - 1) / 25 * ScoreMultiplier))

it becomes clear that that assumption is actually _incorrect_,
and the `ScoreMultiplier` _must_ be applied to every score increase
individually.

The above was cross-checked experimentally against stable source
on an example test map with 100 objects, and a replay hitting them
perfectly.

osu.Game.Tests/Visual/Gameplay/TestSceneScoring.cs

@@ -190,7 +190,9 @@ namespace osu.Game.Tests.Visual.Gameplay
                     return;
                 }
 
-                const float score_multiplier = 1;
+                // this corresponds to stable's `ScoreMultiplier`.
+                // value is chosen arbitrarily, towards the upper range.
+                const float score_multiplier = 4;
 
                 totalScore += baseScore;
 
@@ -208,13 +210,7 @@ namespace osu.Game.Tests.Visual.Gameplay
                 ApplyHit = () => applyHitV1(base_great),
                 ApplyNonPerfect = () => applyHitV1(base_ok),
                 ApplyMiss = () => applyHitV1(0),
-                GetTotalScore = () =>
-                {
-                    // Arbitrary value chosen towards the upper range.
-                    const double score_multiplier = 4;
-
-                    return (int)(totalScore * score_multiplier);
-                },
+                GetTotalScore = () => totalScore,
                 Visible = scoreV1Visible
             });
         }