Remove obsolete bump_gocui.sh script

We copied the gocui sources into lazygit a while ago, so we no longer
need this.

scripts/bump_gocui.sh

@@ -1,7 +0,0 @@
-#!/bin/sh
-
-# Go's proxy servers are not very up-to-date so that's why we use `GOPROXY=direct`
-# We specify the `master` branch to avoid the default behaviour of looking for a semver tag.
-GOPROXY=direct go get -u github.com/jesseduffield/gocui@master && go mod vendor && go mod tidy
-
-# Note to self if you ever want to fork a repo be sure to use this same approach: it's important to use the branch name (e.g. master)