DebugInfo: Remove dead code from old DebugLoc API

DebugInfo: Remove dead code from old DebugLoc API

Remove old API for `DebugLoc` now that all the callers have been
updated.  If this broke your out-of-tree build, here's a quick map from
the old API to the new one:

    DebugLoc DebugLoc::getFromMDLocation(MDNode *)
      => DebugLoc::DebugLoc(MDLocation *)
      => explicit DebugLoc::DebugLoc(MDNode *) // works with broken code

    MDNode *DebugLoc::getAsMDNode(LLVMContext &)
      => MDLocation *DebugLoc::get()
      => DebugLoc::operator MDLocation *()
      => MDNode *DebugLoc::getAsMDNode() // works with broken code

    bool DebugLoc::isUnknown()
      => DebugLoc::operator MDLocation *()
          i.e.: if (MDLocation *DL = ...)
      => DebugLoc::operator bool() // works with broken code
          i.e.: if (DebugLoc DL = ...)

    void DebugLoc::getScopeAndInlinedAt(MDNode *&, MDNode *&)
      => use: MDNode *DebugLoc::getScope()
         and: MDLocation *DebugLoc::getInlinedAt()

    MDNode *DebugLoc::getScopeNode(LLVMContext &)
      => MDNode *DebugLoc::getInlinedAtScope()

    void DebugLoc::dump(LLVMContext &)
      => void DebugLoc::dump()

    void DebugLoc::getFnDebugLoc(LLVMContext &)
      => void DebugLoc::getFnDebugLoc()

    MDNode *DebugLoc::getScope(LLVMContext &)
      => MDNode *DebugLoc::getScope()

    MDNode *DebugLoc::getInlinedAt(LLVMContext &)
      => MDLocation *DebugLoc::getInlinedAt()

I've noted above the only functions that won't crash on broken code (due
to downcasting to `MDLocation`).  If your code could be dealing with
broken IR (i.e., you haven't run the verifier yet, or you've used a
temporary node that will eventually (but not yet) get RAUW'ed to an
`MDLocation`), you need to restrict yourself to those.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233599 91177308-0d34-0410-b5e6-96231b3b80d8