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/expressions/funInterface/basicFunInterfaceConversion.sig.kt.txt

@@ -34,11 +34,4 @@ fun foo(f: Foo): String
 //   Public signature: /test|6620506149988718649[0]
 //   Public signature debug description: test(){}
 fun test(): String
-  // CHECK JVM_IR:
-  //   Mangled name: #test(){}kotlin.String#<anonymous>#static(){}kotlin.String
-  //   Mangled name for the signature: test(){}kotlin.String<anonymous>#static(){}kotlin.String
-  // CHECK JS_IR NATIVE:
-  //   Mangled name: #test(){}#<anonymous>#static(){}
-  //   Mangled name for the signature: test(){}<anonymous>#static(){}
-  local fun <anonymous>(): String