Revert "GlobalISel: Add G_ASSERT_ALIGN hint instruction"

This commit sometimes causes a crash when compiling a vtable thunk. E.g.:

clang '--target=aarch64-grtev4-linux-gnu' -xc++ - -c -o /dev/null <<EOF
struct a {
  virtual int f();
};
struct c {
  virtual int &g() const;
};
struct d : a, c {
  int &g() const;
};
int &d::g() const {}
EOF

Some follow-up commits have been reverted as well:
Revert "IR: Make getRetAlign check callee function attributes"
Revert "Fix MSVC "32-bit shift implicitly converted to 64 bits" warning. NFC."
Revert "Fix MSVC "32-bit shift implicitly converted to 64 bits" warning. NFC."

This reverts commit 4f414af6.
This reverts commit a5507d2e.
This reverts commit 3d2d208f.
This reverts commit 07ddfa95.