FIR2IR: fix generation of source overridden symbols

This commit makes source overridden and f/o overridden consistent.

compiler/testData/ir/irText/firProblems/AbstractMutableMap.fir.ir.txt

@@ -12,7 +12,6 @@ FILE fqName:<root> fileName:/AbstractMutableMap.kt
     FUN name:put visibility:public modality:FINAL <> ($this:<root>.MyMap<K of <root>.MyMap, V of <root>.MyMap>, key:K of <root>.MyMap, value:V of <root>.MyMap) returnType:V of <root>.MyMap?
       overridden:
         public abstract fun put (key: K of kotlin.collections.AbstractMutableMap, value: V of kotlin.collections.AbstractMutableMap): V of kotlin.collections.AbstractMutableMap? declared in kotlin.collections.AbstractMutableMap
-        public open fun put (p0: @[FlexibleNullability] K of kotlin.collections.AbstractMutableMap?, p1: @[FlexibleNullability] V of kotlin.collections.AbstractMutableMap?): V of kotlin.collections.AbstractMutableMap? [fake_override] declared in kotlin.collections.AbstractMutableMap
       $this: VALUE_PARAMETER name:<this> type:<root>.MyMap<K of <root>.MyMap, V of <root>.MyMap>
       VALUE_PARAMETER name:key index:0 type:K of <root>.MyMap
       VALUE_PARAMETER name:value index:1 type:V of <root>.MyMap

compiler/testData/ir/irText/firProblems/ArrayListOverrides.fir.ir.txt

@@ -203,8 +203,6 @@ FILE fqName:<root> fileName:/ArrayListOverrides.kt
     FUN name:remove visibility:public modality:FINAL <> ($this:<root>.A2, x:kotlin.String) returnType:kotlin.Boolean
       overridden:
         public open fun remove (p0: @[EnhancedNullability] E of java.util.ArrayList): kotlin.Boolean declared in java.util.ArrayList
-        public open fun remove (p0: @[FlexibleNullability] E of java.util.ArrayList?): kotlin.Boolean [fake_override] declared in java.util.ArrayList
-        public abstract fun remove (element: E of java.util.ArrayList): kotlin.Boolean [fake_override] declared in java.util.ArrayList
       $this: VALUE_PARAMETER name:<this> type:<root>.A2
       VALUE_PARAMETER name:x index:0 type:kotlin.String
       BLOCK_BODY