Revert "[ExecutionEngine] Allow JIT tests to run on PowerPC."

This reverts commit d771f54107 due to builder
failures, e.g. https://lab.llvm.org/buildbot#builders/93/builds/14488.

llvm/test/ExecutionEngine/lit.local.cfg

@@ -1,4 +1,4 @@
-if config.root.native_target in ['Sparc', 'SystemZ', 'Hexagon', 'RISCV']:
+if config.root.native_target in ['Sparc', 'PowerPC', 'SystemZ', 'Hexagon', 'RISCV']:
     config.unsupported = True
 
 # ExecutionEngine tests are not expected to pass in a cross-compilation setup.