Revert "Use gdk Bash shim by default"

What does this merge request do and why?

This reverts !2881 (merged) as it's causing one-line-install job to fail: #1656 (closed):

INFO: To make sure GDK commands are available in this shell, run:
source "/home/gdk/.asdf/asdf.sh"
/home/gdk/.asdf/installs/ruby/3.0.5/lib/ruby/site_ruby/3.0.0/rubygems.rb:265:in `find_spec_for_exe': can't find gem gitlab-development-kit (>= 0.a) with executable gdk (Gem::GemNotFoundException)
	from /home/gdk/.asdf/installs/ruby/3.0.5/lib/ruby/site_ruby/3.0.0/rubygems.rb:284:in `activate_bin_path'
	from /home/gdk/.asdf/installs/ruby/3.0.5/bin/gdk:25:in `<main>'

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.