[clang][test] zero-init-empty-virtual.cpp: remove redundant alignment check
Fixes a `clang-armv8-quick` buildbot failure. Where the alignment
was `4` instead of `8`:
```
// CHECK: @{{.*}} = {{.*}}global %struct.Holder2 zeroinitializer, align 8
^
<stdin>:66:178: note: scanning from here
@g_holder1 = global %struct.Holder1 { %struct.polymorphic_base { ptr getelementptr inbounds inrange(-8, 12) ({ [5 x ptr] }, ptr @_ZTV16polymorphic_base, i32 0, i32 0, i32 2) } }, align 4
^
<stdin>:68:8: note: possible intended match here
@g_holder2 = global %struct.Holder2 zeroinitializer, align 4
^
```
This test isn't about checking alignment, so remove that from the
FileCheck entry.