Remove lshr-constexpr.ll test after 56c1d30 (#2215)

https://discourse.llvm.org/t/rfc-remove-most-constant-expressions/63179 is being implemented, and some tests become obsolete.

Signed-off-by: Sidorov, Dmitry <dmitry.sidorov@intel.com>

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@2075517

Author: MrSidims