Remove unused defined_names and simplify contains return

- Remove unused 'defined_names dn(m)' variable in smt_model_checker.cpp,
  a leftover from the 'remove side definitions' refactoring
- Remove corresponding unused #include of defined_names.h from smt_model_checker.h
- Simplify redundant if/return pattern in fingerprint_set::contains to
  a direct return statement

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/smt/fingerprints.cpp

@@ -100,13 +100,11 @@ namespace smt {
 
     bool fingerprint_set::contains(void * data, unsigned data_hash, unsigned num_args, enode * const * args) {
         fingerprint * d = mk_dummy(data, data_hash, num_args, args);
-        if (m_set.contains(d)) 
+        if (m_set.contains(d))
             return true;
         for (unsigned i = 0; i < num_args; ++i)
             d->m_args[i] = d->m_args[i]->get_root();
-        if (m_set.contains(d))
-            return true;
-        return false;
+        return m_set.contains(d);
     }
     
     void fingerprint_set::reset() {

src/smt/smt_model_checker.cpp

@@ -258,7 +258,6 @@ namespace smt {
                 svector<symbol> names;
                 for (unsigned i = 0; i < f->get_arity(); ++i) 
                     names.push_back(symbol(i));
-                defined_names dn(m);
                 body = replace_value_from_ctx(body);
                 body = m.mk_lambda(sorts.size(), sorts.data(), names.data(), body);
                 sk_term = body;

src/smt/smt_model_checker.h

@@ -23,7 +23,6 @@ Revision History:
 #include "util/obj_hashtable.h"
 #include "ast/ast.h"
 #include "ast/array_decl_plugin.h"
-#include "ast/normal_forms/defined_names.h"
 #include "params/qi_params.h"
 #include "params/smt_params.h"