Revert "[Offload] Run unit tests as a part of check-offload" (#157346)

Reverts #156675 due to regressions in standalone build
and test errors without all plugins enabled (#157345).

Author: mgorny

offload/test/CMakeLists.txt

@@ -61,7 +61,7 @@ add_offload_testsuite(check-offload
   "Running libomptarget tests"
   ${LIBOMPTARGET_LIT_TESTSUITES}
   EXCLUDE_FROM_CHECK_ALL
-  DEPENDS llvm-offload-device-info omptarget ${OMP_DEPEND} ${LIBOMPTARGET_TESTED_PLUGINS} check-offload-unit
+  DEPENDS llvm-offload-device-info omptarget ${OMP_DEPEND} ${LIBOMPTARGET_TESTED_PLUGINS}
   ARGS ${LIBOMPTARGET_LIT_ARG_LIST})
 
 # Add liboffload unit tests - the test binary will run on all available devices