[opaque pointer types] Remove some calls to generic Type subtype accessors.

That is, remove many of the calls to Type::getNumContainedTypes(),
Type::subtypes(), and Type::getContainedType(N).

I'm not intending to remove these accessors -- they are
useful/necessary in some cases. However, removing the pointee type
from pointers would potentially break some uses, and reducing the
number of calls makes it easier to audit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350835 91177308-0d34-0410-b5e6-96231b3b80d8
13 files changed