As of d0052ebbe2 the setUpGenericLLVMIRPlatform function will automatically
add an instance of the EHFrameRegistrationPlugin (for LLJIT instances whose
object linking layers are ObjectLinkingLayers, not RTDyldObjectLinkingLayers).
This commit removes the redundant plugin creation in the object linking
layer constructor function in lli.cpp to prevent duplicate registration of
eh-frames, which is likely the cause of recent bot failures, e.g.
https://lab.llvm.org/buildbot/#/builders/108/builds/8685.