plugin(dirs): remove shopt -s cdable_vars

[davidpfarrell]

Removes shopt setings from dirs plugin

Description

Remove thes shopt -s cdable_vars setting from the dirs plugin.

Motivation and Context

I decided that I no-longer wanted cdable_vars enabled as I have too many environment variables and they were constantly getting in the way of tab-completing cd.

After removing the option from the my local bash config (I had it explicitly enabled), I discovered that it was STILL enabled when launching a new terminal.

I tracked it down to this plugin.

As much as possible, shopt settings should be left to the user.

Additionally, this plugin does not require the cdable_vars be enabled.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Marking as Breaking Change since some users may have picked up the setting from this plugin and may not realize why its missing after their next update.

[NoahGorny]

Lgtm