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/firProblems/DelegationAndInheritanceFromJava.sig.kt.txt

@@ -7,11 +7,6 @@ class Impl : A, B {
   //   Public signature: /Impl.<init>|1084968671839233134[0]
   //   Public signature debug description: <init>(Foo.B){}
   constructor(b: B) /* primary */
-  // CHECK:
-  //   Mangled name: Impl.$$delegate_0
-  //   Public signature: /Impl.$$delegate_0|-7286425919675154353[0]
-  //   Public signature debug description: 
-  private /* final field */ val $$delegate_0: B
   // CHECK JVM_IR:
   //   Mangled name: Impl#add(kotlin.String?){}kotlin.Boolean
   //   Public signature: /Impl.add|-2525808668243873976[0]