bug#36250: Allow Emacs to be resized arbitrarily

[Konstantin Kharlamov <hi-angel@yandex.ru>]

For a long time Emacs was setting PResizeInc flag for WM_SIZE_HINTS, 
thus causing problems to users of standard-compliant window managers, 
such as not being able to open Emacs in fullscreen¹ or not being able 
to resize Emacs to fill all free space on the screen².

I investigated reasons why these variables were set in the first place, 
and found the first occurrence of `size_hints.width_inc` in `xterm.c`, 
commit `Initial revision` in 1991 year, function `x_wm_set_size_hint`. 
First occurrence in GTK related file is at `gtkutil.c`, commit `GTK 
files gtkutil.c and .h` in 2003. Both commits lack any description, and 
no comments on the resize matter provided.

This patch fixes the problem, the property "program specified resize 
increment" in `xprop` output is no longer set.

Unconstrained resize of Emacs is widely tested, e.g. I've been using 
for years Emacs on i3wm, which just ignores the property, thus resizes 
Emacs arbitrarily. Also: I don't touch in this patch 
`frame_resize_pixelwise` variable, because it's used for something 
else; in particular, setting this variable had no influence on the 
problem.

1: https://bugs.kde.org/show_bug.cgi?id=408746#c8
2: https://github.com/kwin-scripts/kwin-tiling/issues/161