[ELF] Remove unnecessary function call. NFC.
[ELF] Remove unnecessary function call. NFC.

StringTableSection does not implement postThunkContents, so calling it on these 
sections is pointless (it calls an empty virtual function), and we can remove it.

Reviewers: ruiu

Differential Revision: https://reviews.llvm.org/D39460

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@317014 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld