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/classes/implicitNotNullOnDelegatedImplementation.kt

@@ -1,7 +1,7 @@
 // TARGET_BACKEND: JVM
 
-// MUTE_SIGNATURE_COMPARISON_K2: ANY
-// ^ KT-57788
+// MUTE_SIGNATURE_COMPARISON_K2: JVM_IR
+// ^ KT-57788: Fix computing mangled names of types with @EnhancedNullability from IR-based declaration descriptors
 
 // FILE: implicitNotNullOnDelegatedImplementation.kt
 interface IFoo {