remove Git pre-commit hook for make check-strings

[cfm]

Description

In freedomofpress/securedrop#6232, we wound up deciding against using a pre-commit hook to enforce make check-strings, entrusting this instead to CI.

For consistency, let's remove this hook here too.

How will this impact SecureDrop users?

No user-facing implications.

How would this affect the SecureDrop Workstation threat model?

No threat-model implications.

User Stories

As a SecureDrop contributor, I want the development experiences between the SecureDrop Server and Client to be as similar as possible.