[FIR2IR] Drop effectively unused FirMetadataSource.File.descriptors

NB: only FileClassLowering uses this property to check
whether facade is required, and IR-based check is enough in this lowering

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrVisitor.kt

@@ -87,7 +87,7 @@ class Fir2IrVisitor(
                 it.accept(this@Fir2IrVisitor, data) as? IrConstructorCall
             }
 
-            (this as IrFileImpl).metadata = FirMetadataSource.File(file, components.session, declarations.map { it.descriptor })
+            (this as IrFileImpl).metadata = FirMetadataSource.File(file, components.session)
         }
     }
 

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/FirMetadataSource.kt

@@ -18,8 +18,8 @@ interface FirMetadataSource : MetadataSource {
     val session: FirSession
 
     class File(
-        val file: FirFile, override val session: FirSession, descriptors: List<DeclarationDescriptor>
-    ) : MetadataSource.File(descriptors), FirMetadataSource
+        val file: FirFile, override val session: FirSession
+    ) : MetadataSource.File(emptyList()), FirMetadataSource
 
     class Class(
         val klass: FirClass<*>, descriptor: WrappedClassDescriptor