Deprecate several locale functions

Problem/Motivation

Let's convert and deprecate:

• locale_translation_use_remote_source
• locale_string_is_safe
• locale_translatable_language_list
• locale_js_translate
• locale_translation_language_table
• locale_is_translatable

Steps to reproduce

Open locale.module

Proposed resolution

Convert them more info incoming

Remaining tasks

User interface changes

N/A

Introduced terminology

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

N/A