Revert r350917 "[Sema] If CheckPlaceholderExpr rewrites the initializer

Revert r350917 "[Sema] If CheckPlaceholderExpr rewrites the initializer
of an auto"

This commit changed the initializer expression passed into
initialization (stripping off an enclosing pair of parentheses or
braces) and subtly changing the meaning of programs, typically by
inserting bogus calls to copy constructors.

See the added testcase in test/SemaCXX/cxx1y-init-captures.cpp for an
example of the breakage.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@359066 91177308-0d34-0410-b5e6-96231b3b80d8