Remove InitialiseLocale()

[Ortham]

InitialiseLocale() was previously used to set the locale for:

• creating path objects from UTF-8 strings when using Boost.Filesystem - std::filesystem handles encoding differently, and libloot uses u8path for UTF-8 support instead of relying on the current global locale.
• boost::locale::to_lower() - this is currently used by PluginMetadata::GetLowercasedName(), which will be removed as part of #53.
• boost::locale::to_upper() - this is currently used by CompareFilenames() and NormalizeFilename() on Linux, but #54 will switch to using ICU.

So once #53 and #54 are done, there will be no need for InitialiseLocale(), which will simplify using libloot.

[Ortham]

Done in 8b0c057ca3f9db42ae72eea6ba74fc8c82fb1ad2.