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/contextReceiverMethod.sig.kt.txt

@@ -29,15 +29,6 @@ class Test {
   //   Public signature: /Test.<init>|4848133296495274545[0]
   //   Public signature debug description: <init>!Context(){}
   constructor($context_receiver_0: Context) /* primary */
-  // CHECK JVM_IR:
-  //   Mangled name: Test.contextReceiverField0
-  //   Mangled name for the signature computed from Ir:
-  //   Mangled name for the signature computed from Descriptor: {}contextReceiverField0#jf
-  // CHECK JS_IR NATIVE:
-  //   Mangled name: Test.contextReceiverField0
-  //   Mangled name for the signature computed from Ir:
-  //   Mangled name for the signature computed from Descriptor: {}contextReceiverField0
-  private /* final field */ val contextReceiverField0: Context
 
   // CHECK:
   //   Mangled name: Test#bar(){}