[JVMCI] fix JVMCI jtreg events tests to work with GraalVM

The compiler/jvmci/events jtreg tests specify an explicit value for -Djvmci.Compiler which causes a problem when run on GraalVM.
For example:

Exception during HotSpotJVMCIRuntime initialization:
Exception in thread "main": jdk.vm.ci.common.JVMCIError
jdk.vm.ci.common.JVMCIError: JVMCI compiler 'EmptyCompiler' not found
at jdk.vm.ci.hotspot.HotSpotJVMCICompilerConfig.getCompilerFactory(HotSpotJVMCICompilerConfig.java:99)
at jdk.vm.ci.hotspot.HotSpotJVMCIRuntime.<init>(HotSpotJVMCIRuntime.java:468)
at jdk.vm.ci.hotspot.HotSpotJVMCIRuntime.runtime(HotSpotJVMCIRuntime.java:172)
at com.oracle.svm.jni.JNIJavaCallWrappers.jniInvoke_VA_LIST:Ljdk_vm_ci_hotspot_HotSpotJVMCIRuntime_2_0002eruntime_00028_00029Ljdk_vm_ci_hotspot_HotSpotJVMCIRuntime_2(JNIJavaCallWrappers.java:0)
at jdk.vm.ci.runtime.JVMCI.initializeRuntime(JVMCI.java)
at jdk.vm.ci.runtime.JVMCI.getRuntime(JVMCI.java:65)
at com.oracle.svm.jni.JNIJavaCallWrappers.jniInvoke_VA_LIST:Ljdk_vm_ci_runtime_JVMCI_2_0002egetRuntime_00028_00029Ljdk_vm_ci_runtime_JVMCIRuntime_2(JNIJavaCallWrappers.java:0)

The problem is that GraalVM includes and enables libgraal by default and only the JVMCI compilers in libgraal will be matched against the jvmci.Compiler value. The solution is to disable UseJVMCINativeLibrary for these tests.