kill unused kp_newuserdata function and ktap_udata strucutre

There have no user for kp_newuserdata and ktap_udata, so kill it.

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>
create synth_tbl in kp_aggrtable_new

This will avoid create synth_tbl multiple times when
using histogram or pairs of aggregation table.

Further more, we only allow create table in mainthread.

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>
cleanup some comments associated with lua

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>
rename ktap_aggrtable to ktap_ptable

Use a more simple name to represent parallel table.

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>