[MC] Clean up unused inline function and non-anchor defaulted destructors; NFCI

Take care of some missing clean-ups that belong with r249548 and some
other copy/paste that had happened. In particular, the destructors are
no longer vtable anchors after r249548; and `setSectionName` in
`MCSectionWasm` is private and unused since r313058 culled its only
caller. The destructors are now implicitly defined, and the unused
function is removed.

Reviewers: nemanjai, jasonliu, grosbach

Reviewed By: nemanjai

Subscribers: sbc100, aheejin, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57182

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353597 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed