Revert std::move on returned local variables - prevents copy elision

Co-authored-by: nunoplopes <2998477+nunoplopes@users.noreply.github.com>

src/muz/transforms/dl_mk_synchronize.cpp

@@ -169,9 +169,9 @@ namespace datalog {
                     dst_vector.push_back(new_rule.get());
                 }
             }
-            result.push_back(std::move(dst_vector));
+            result.push_back(dst_vector);
         }
-        return std::move(result);
+        return result;
     }
 
     void mk_synchronize::add_rec_tail(vector< ptr_vector<app> > & recursive_calls,

src/opt/opt_preprocess.cpp

@@ -146,7 +146,7 @@ namespace opt {
         for (expr* f : fmls)
             fmls[i++] = mk_not(m, f);
 
-        return std::move(new_soft);
+        return new_soft;
     }
 
     bool preprocess::find_mutexes(vector<soft>& softs, rational& lower) {

src/qe/qe_mbi.cpp

@@ -333,7 +333,7 @@ namespace qe {
         (void)ok;
         CTRACE(qe, !ok, tout << "projection failure ignored!!!!\n");
         fix_non_shared(*mdl, lits);
-        return std::move(defs);
+        return defs;
     }
 
     mbi_result uflia_mbi::operator()(expr_ref_vector& lits, model_ref& mdl) {

src/sat/smt/fpa_solver.cpp

@@ -78,7 +78,7 @@ namespace fpa {
             conds.push_back(mk_literal(t));
         }
         m_converter.m_extra_assertions.reset();
-        return std::move(conds);
+        return conds;
     }
 
     sat::check_result solver::check() {

src/smt/theory_datatype.cpp

@@ -695,7 +695,7 @@ namespace smt {
         for (enode* n : f) 
             result.push_back(n);        
         f.reset();
-        return std::move(result);
+        return result;
     }
 
     void theory_datatype::relevant_eh(app * n) {

src/solver/solver_pool.cpp

@@ -351,7 +351,7 @@ ptr_vector<solver> solver_pool::get_base_solvers() const {
             solvers.push_back(s->base_solver());
         }
     }
-    return std::move(solvers);
+    return solvers;
 }
 
 void solver_pool::updt_params(const params_ref &p) {