[SYCL] Remove unnecessary llvm-spirv substitution (intel#341)

Note: this is a cherry-pick of intel-llvm/llvm-test-suite intel#540.

Remove a tool substitution which effectively assumes that llvm-spirv is
in sycl_tools_dir. If it's not, the substitution results in an incorrect
absolute path, preventing llvm-spirv from being found elsewhere via
PATH. If llvm-spirv is in sycl_tools_dir the removed substitution
unnecessary because we also add sycl_tools_dir to PATH.

Author: tcreech-intel

SYCL/lit.cfg.py

@@ -149,8 +149,6 @@
     config.substitutions.append( ('%debug_option',  '-g' ) )
     config.substitutions.append( ('%cxx_std_option',  '-std=' ) )
 
-llvm_config.add_tool_substitutions(['llvm-spirv'], [config.sycl_tools_dir])
-
 if not config.sycl_be:
      lit_config.error("SYCL backend is not specified")