[FIR] builder: drop unused forcedElementSourceKind

There was only one usage by withDefaultSourceElementKind that was
dropped in the previous commit

^KT-63042

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/converter/AbstractLightTreeRawFirBuilder.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -31,7 +31,7 @@ abstract class AbstractLightTreeRawFirBuilder(
     override fun LighterASTNode.toFirSourceElement(kind: KtFakeSourceElementKind?): KtLightSourceElement {
         val startOffset = tree.getStartOffset(this)
         val endOffset = tree.getEndOffset(this)
-        return toKtLightSourceElement(tree, kind ?: context.forcedElementSourceKind ?: KtRealSourceElementKind, startOffset, endOffset)
+        return toKtLightSourceElement(tree, kind ?: KtRealSourceElementKind, startOffset, endOffset)
     }
 
     override val LighterASTNode.elementType: IElementType

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/converter/LightTreeRawFirExpressionBuilder.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -78,7 +78,7 @@ class LightTreeRawFirExpressionBuilder(
                 )
             }
             else -> buildErrorExpression(
-                converted?.source?.withForcedKindFrom(context) ?: expression?.toFirSourceElement(),
+                converted?.source?.realElement() ?: expression?.toFirSourceElement(),
                 if (expression == null) ConeSyntaxDiagnostic(errorReason)
                 else ConeSimpleDiagnostic(errorReason, DiagnosticKind.ExpressionExpected),
                 converted,