[FIR] Consolidate SYNTAX and SYNTAX_WITH_MESSAGE diagnostics

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -5083,12 +5083,6 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
     }
     add(FirSyntaxErrors.SYNTAX) { firDiagnostic ->
         SyntaxImpl(
-            firDiagnostic as KtPsiDiagnostic,
-            token,
-        )
-    }
-    add(FirSyntaxErrors.SYNTAX_WITH_MESSAGE) { firDiagnostic ->
-        SyntaxWithMessageImpl(
             firDiagnostic.a,
             firDiagnostic as KtPsiDiagnostic,
             token,

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -3539,10 +3539,6 @@ sealed class KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
 
     abstract class Syntax : KtFirDiagnostic<PsiElement>() {
         override val diagnosticClass get() = Syntax::class
-    }
-
-    abstract class SyntaxWithMessage : KtFirDiagnostic<PsiElement>() {
-        override val diagnosticClass get() = SyntaxWithMessage::class
         abstract val message: String
     }
 

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -4279,13 +4279,8 @@ internal class WrongOperationWithDynamicImpl(
 ) : KtFirDiagnostic.WrongOperationWithDynamic(), KtAbstractFirDiagnostic<KtElement>
 
 internal class SyntaxImpl(
+    override val message: String,
     override val firDiagnostic: KtPsiDiagnostic,
     override val token: KtLifetimeToken,
 ) : KtFirDiagnostic.Syntax(), KtAbstractFirDiagnostic<PsiElement>
 
-internal class SyntaxWithMessageImpl(
-    override val message: String,
-    override val firDiagnostic: KtPsiDiagnostic,
-    override val token: KtLifetimeToken,
-) : KtFirDiagnostic.SyntaxWithMessage(), KtAbstractFirDiagnostic<PsiElement>
-