Revert "Canonicalize declaration pointers when forming APValues."

This reverts commit 905b9ca2.

Reverting because this strips `weak` attributes off function
declarations, leading to the linker error we see at
https://ci.chromium.org/p/fuchsia/builders/ci/clang_toolchain.fuchsia-arm64-debug-subbuild/b8868932035091473008.

See https://reviews.llvm.org/rG905b9ca26c94 for reproducer details.