build_emoji: Add `setup_old_emoji_farm()` function.
build_emoji: Add `setup_old_emoji_farm()` function.

This commit adds `setup_old_emoji_farm()` function to the build_emoji
script. This will change the way of setting up the old emoji farm.
Earlier we used to extract the glyphs corresponding to each emoji from
the `NotoColorEmoji.ttf` file. But since now we already have individual
images in the new emoji farm(from iamcal's 'emoji-datasource-google' npm
package) we can just symlink old emoji files to the new image files. This
apart from helping us in cleaning up the `build_emoji` script will also
help in reducing the increased size of the release tarball due to the
addition of new emoji farm.

brainwane/zulip,rht/zulip,jackrzhang/zulip,tommyip/zulip,verma-varsha/zulip,andersk/zulip,hackerkid/zulip,timabbott/zulip,Galexrt/zulip,hackerkid/zulip,brockwhittaker/zulip,mahim97/zulip,andersk/zulip,amanharitsh123/zulip,zulip/zulip,jackrzhang/zulip,punchagan/zulip,kou/zulip,synicalsyntax/zulip,showell/zulip,punchagan/zulip,hackerkid/zulip,timabbott/zulip,dhcrzf/zulip,brockwhittaker/zulip,shubhamdhama/zulip,synicalsyntax/zulip,verma-varsha/zulip,jackrzhang/zulip,timabbott/zulip,eeshangarg/zulip,showell/zulip,andersk/zulip,eeshangarg/zulip,tommyip/zulip,punchagan/zulip,hackerkid/zulip,kou/zulip,tommyip/zulip,amanharitsh123/zulip,brainwane/zulip,kou/zulip,showell/zulip,shubhamdhama/zulip,verma-varsha/zulip,timabbott/zulip,brockwhittaker/zulip,Galexrt/zulip,brainwane/zulip,punchagan/zulip,synicalsyntax/zulip,rishig/zulip,kou/zulip,timabbott/zulip,rishig/zulip,verma-varsha/zulip,andersk/zulip,andersk/zulip,jackrzhang/zulip,synicalsyntax/zulip,dhcrzf/zulip,zulip/zulip,mahim97/zulip,Galexrt/zulip,brainwane/zulip,showell/zulip,synicalsyntax/zulip,tommyip/zulip,dhcrzf/zulip,brockwhittaker/zulip,zulip/zulip,hackerkid/zulip,verma-varsha/zulip,punchagan/zulip,hackerkid/zulip,verma-varsha/zulip,rht/zulip,jackrzhang/zulip,rht/zulip,eeshangarg/zulip,dhcrzf/zulip,rht/zulip,andersk/zulip,dhcrzf/zulip,kou/zulip,dhcrzf/zulip,Galexrt/zulip,eeshangarg/zulip,brainwane/zulip,zulip/zulip,tommyip/zulip,rishig/zulip,brockwhittaker/zulip,mahim97/zulip,andersk/zulip,rht/zulip,rishig/zulip,punchagan/zulip,kou/zulip,showell/zulip,Galexrt/zulip,jackrzhang/zulip,mahim97/zulip,jackrzhang/zulip,brainwane/zulip,shubhamdhama/zulip,brockwhittaker/zulip,zulip/zulip,kou/zulip,shubhamdhama/zulip,timabbott/zulip,eeshangarg/zulip,tommyip/zulip,hackerkid/zulip,shubhamdhama/zulip,synicalsyntax/zulip,showell/zulip,tommyip/zulip,mahim97/zulip,Galexrt/zulip,rishig/zulip,amanharitsh123/zulip,rht/zulip,punchagan/zulip,amanharitsh123/zulip,shubhamdhama/zulip,zulip/zulip,Galexrt/zulip,eeshangarg/zulip,synicalsyntax/zulip,rishig/zulip,shubhamdhama/zulip,amanharitsh123/zulip,dhcrzf/zulip,showell/zulip,rishig/zulip,amanharitsh123/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,mahim97/zulip,brainwane/zulip,timabbott/zulip