FIR2IR: don't generate unnecessary 'return throw'

#KT-60245 Fixed

compiler/testData/ir/irText/expressions/kt30796.fir.ir.txt

@@ -2,9 +2,8 @@ FILE fqName:<root> fileName:/kt30796.kt
   FUN name:magic visibility:public modality:FINAL <T> () returnType:T of <root>.magic
     TYPE_PARAMETER name:T index:0 variance: superTypes:[kotlin.Any?] reified:false
     BLOCK_BODY
-      RETURN type=kotlin.Nothing from='public final fun magic <T> (): T of <root>.magic declared in <root>'
-        THROW type=kotlin.Nothing
-          CONSTRUCTOR_CALL 'public constructor <init> () declared in java.lang.Exception' type=java.lang.Exception origin=null
+      THROW type=kotlin.Nothing
+        CONSTRUCTOR_CALL 'public constructor <init> () declared in java.lang.Exception' type=java.lang.Exception origin=null
   FUN name:test visibility:public modality:FINAL <T> (value:T of <root>.test, value2:T of <root>.test) returnType:kotlin.Unit
     TYPE_PARAMETER name:T index:0 variance: superTypes:[kotlin.Any?] reified:false
     VALUE_PARAMETER name:value index:0 type:T of <root>.test

compiler/testData/ir/irText/expressions/kt30796.fir.kt.txt

@@ -1,5 +1,5 @@
 fun <T : Any?> magic(): T {
-  return throw Exception()
+  throw Exception()
 }
 
 fun <T : Any?> test(value: T, value2: T) {