Remove unneeded type conversions in spellchecker_hunspell.cpp

[0tkl]

Since v1.5 (released in Nov. 2016), Hunspell has deprecated C style APIs and added a new set of C++ APIs.
https://github.com/hunspell/hunspell/compare/v1.4.2...v1.5.3#diff-4c6057a8b7a2e93a0c4e414dfc8ca7cc527ab00ba2b909622bf0d3591fc146b4

Some conversions in spellchecker_hunspell.cpp are no longer needed.
GetSuggestions(), with hunspell->suggest() in it, had been refactored in Plork's modernization.