Do not use std-invariants with k-induction

Standard invariants seem to cause more trouble than with array
invariants (already fixed). Let us try to disable them completely since
they should bring no significant benefits.

There are some tests which still require standard invariants with
k-induction. Add the option explicitly and we will debug them later.

Author: viktormalik

regression/kiki/induction5/test.desc

@@ -1,6 +1,6 @@
 CORE
 main.c
---k-induction
+--k-induction --std-invariants
 ^EXIT=10$
 ^SIGNAL=0$
 ^.*FAILURE$

regression/kiki/induction7/test.desc

@@ -1,6 +1,6 @@
 CORE
 main.c
---k-induction
+--k-induction --std-invariants
 ^EXIT=10$
 ^SIGNAL=0$
 ^.*FAILURE$

regression/kiki/nested12/test.desc

@@ -1,6 +1,6 @@
 CORE
 main.c
---k-induction
+--k-induction --std-invariants
 ^EXIT=10$
 ^SIGNAL=0$
 ^.*FAILURE$

src/2ls/2ls_parse_options.cpp

@@ -296,7 +296,6 @@ void twols_parse_optionst::get_command_line_options(optionst &options)
   // do k-induction refinement
   if(cmdline.isset("k-induction"))
   {
-    options.set_option("std-invariants", true);
     options.set_option("k-induction", true);
     options.set_option("inline", true);
     if(!cmdline.isset("unwind"))