Removed unused gensym_allowing_implicit, making gensyms simpler.
Removed env parameter of rewrite_term_t rewrite functions, used hard-coded gensyms.
Added unreachable\(\) case for final_wrap.
Made obj_or_seq_op_term_t use hard-coded gensym.
Made use of hard-coded gensyms in val.cc.
Removed the now unused type symgen_t.