[lang] Uniformize "not available" string usage

[hudokkow]

Description

• N/A, Not available, Unavailable and ? are now Not available except where N/A is requested (CSysInfo::GetHddSpaceInfo).
• Removed hardcoded N/A except on CCPUInfo. Will be dealt with later.
• Made N/A translatable. In my native language that would be N/D
• Deprecated a couple of very low strings (161 and 416) but kept them because they might be used by older skins.

What's the policy? Drop deprecated strings completely and force the use of the new string?

Motivation and Context

Noticed this while looking at CSysInfoand CCPUInfo spaghetti.

How Has This Been Tested?

Run time tested under Ubuntu and Win x64.

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed

[MartijnKaijser]

Drop deprecated strings completely and force the use of the new string?

Drop :)

[hudokkow]

Thanks @MartijnKaijser