Revert "Solution Entities" (#23160)

Revert "Solution Entities (#21916)"

This reverts commit d75e743dd7.

Content.Server/Body/Components/LungComponent.cs

@@ -8,7 +8,7 @@ namespace Content.Server.Body.Components;
 [RegisterComponent, Access(typeof(LungSystem))]
 public sealed partial class LungComponent : Component
 {
-    [DataField]
+    [DataField("air")]
     [Access(typeof(LungSystem), Other = AccessPermissions.ReadExecute)] // FIXME Friends
     public GasMixture Air { get; set; } = new()
     {
@@ -16,15 +16,7 @@ public sealed partial class LungComponent : Component
         Temperature = Atmospherics.NormalBodyTemperature
     };
 
-    /// <summary>
-    /// The name/key of the solution on this entity which these lungs act on.
-    /// </summary>
-    [DataField]
-    public string SolutionName = LungSystem.LungSolutionName;
-
-    /// <summary>
-    /// The solution on this entity that these lungs act on.
-    /// </summary>
-    [DataField]
-    public Entity<SolutionComponent>? Solution = null;
+    [ViewVariables]
+    [Access(typeof(LungSystem), Other = AccessPermissions.ReadExecute)] // FIXME Friends
+    public Solution LungSolution = default!;
 }