IR text tests: Don't dump signatures for local declarations

1. Local declarations don't participate in IR-linkage, because they
can be referenced only inside the same body -> can be dropped
from IR text tests.

2. Mangled names for private declarations computed by descriptors/fir
are actually not used anywhere (they are recomputed by IR
immediately before serialization of IR). But sometimes such
mangled names diverge between K1 and K2 -> don't check them, but
always check mangled names computed by IR even for private
declarations.

3. Also: Drop DUMP_LOCAL_DECLARATION_SIGNATURES test directive.

^KT-57428 Obsolete
^KT-57430 Obsolete
^KT-57434 Obsolete
^KT-57778 Obsolete
^KT-57775 Obsolete

compiler/testData/ir/irText/declarations/contextReceivers/function.sig.kt.txt

@@ -7,7 +7,6 @@ class C {
   //   Public signature: /C.c|-4416962153448040627[0]
   //   Public signature debug description: {}c
   val c: Int
-    field
     // CHECK JVM_IR:
     //   Mangled name: C#<get-c>(){}kotlin.Int
     //   Public signature: /C.c.<get-c>|-2440337234483931882[0]
@@ -31,10 +30,6 @@ class C {
 //   Public signature: /bar|-380723744805794672[0]
 //   Public signature debug description: bar(C){}
 fun bar(c: C): Unit
-  // CHECK:
-  //   Mangled name: #bar(C){}#<anonymous>#static@C(){}
-  //   Mangled name for the signature: bar(C){}<anonymous>#static@C(){}
-  local fun C.<anonymous>(): Unit
 
 // CHECK:
 //   Mangled name: #foo!C(){}