[sanitizer] Simplify interceptors with user callbacks.

Get rid of the context argument in UNPOISON_PARAM and INITIALIZE_RANGE.
Get rid of all the thread-local contexts in interceptors.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@203119 91177308-0d34-0410-b5e6-96231b3b80d8