Revert "Allow wish interpreter to be defined with TCLTK_PATH"

Revert "Allow wish interpreter to be defined with TCLTK_PATH"

This reverts commit e2a1bc67d321a0c03737179f331c39a52e7049d7.

Junio rightly pointed out this patch doesn't handle the
`make install` target very well:

Junio C Hamano <junkio@cox.net> writes:
> You should never generate new files in the source tree from
> 'install' target.  Otherwise, the usual pattern of "make" as
> yourself and then "make install" as root would not work from a
> "root-to-nobody-squashing" NFS mounted source tree to local
> filesystem.  You should know better than accepting such a patch.