Revert "fix section size from numberOfSectionsInTableView"

Cause of #185 PR was due to RubyMotion's bug.
and It was fixed in RubyMotiom 2.4.

> RubyMotion 2.4 release notes (/Library/RubyMotion/NEWS)
> * Fixed a bug in Kernel#Array() where it would return an incorrected value
>   if an NSArray object was passed as argument.

I think good to revert #185 PR.
What do you think?