Reduce ide/coq.png to 256x256.
Reduce ide/coq.png to 256x256.

Commit 1774a87 increased the file to 1024x1024. This had two adverse
consequences. First, the icon was too large to be used as a window icon
("gdk_window_set_icon_list: icons too large"), so Coqide 8.5 no longer had
an icon at runtime. Second, the file was also used in the About message
box, which was thus exceeding the display size of any reasonably-priced
device. This commit reverts the file to a saner size (still larger than
the original 66x100 picture).

mattam82/coq,coq/coq,ppedrot/coq,JasonGross/coq,amintimany/coq,letouzey/coq-wip,Lionel-Rieg/coq,letouzey/coq-wip,gares/coq,ejgallego/coq,maximedenes/coq,Ptival/coq,gares/coq,ejgallego/coq,ppedrot/coq,maximedenes/coq,silene/coq,Zimmi48/coq,letouzey/coq-wip,maximedenes/coq,Ptival/coq,gares/coq,Matafou/coq,ejgallego/coq,william-lawvere/coq,JasonGross/coq,Lionel-Rieg/coq,letouzey/coq-wip,silene/coq,letouzey/coq-wip,Zimmi48/coq,mattam82/coq,JasonGross/coq,SkySkimmer/coq,amintimany/coq,ppedrot/coq,Matafou/coq,silene/coq,ppedrot/coq,maximedenes/coq,JasonGross/coq,Ptival/coq,william-lawvere/coq,Zimmi48/coq,Zimmi48/coq,ppedrot/coq,mattam82/coq,maximedenes/coq,coq/coq,Matafou/coq,coq/coq,gares/coq,gares/coq,ejgallego/coq,Lionel-Rieg/coq,william-lawvere/coq,SkySkimmer/coq,coq/coq,SkySkimmer/coq,amintimany/coq,SkySkimmer/coq