fix(completions): remove stray backslashes

[aidandenlinger]

Grep 3.8 causes warnings on regular expressions with stray backslashes:

Regular expressions with stray backslashes now cause warnings, as
their unspecified behavior can lead to unexpected results.
For example, '\a' and 'a' are not always equivalent
https://bugs.gnu.org/39678... The warnings are intended as a
transition aid; they are likely to be errors in future releases.

On a fresh Fedora 38 container with grep 3.8, this results in warnings showing up in the terminal when trying to use the bash completions:

I can't say why these particular backslashes are stray backslashes, but removing them results in the completions working without any errors:

[PThorpe92]

Although the current completions worked for me with a fresh bash setup (I normally use nu or fish), I tested this and it works as expected. So if it works for both sets of users, then LGTM 👍

Thanks for your contribution :)