[#2207] Removed unnecessary null check

STACK Output:
bug: anti-dce
model: |
  %tobool = icmp ne %class.native_auth_plugin* %7, null, !dbg !1628
  -->  true
  ************************************************************
  if.then:
  call void (i32, i8*, ...)* @rodsLog(i32 3, i8* getelementptr inbounds ([52 x i8]* @.str62, i32 0, i32 0)), !dbg !1630
  br label %return, !dbg !1632
stack:
  - /home/kellerb/software/root-stack/irods/plugins/auth/native/libnative.cpp:615:0
ncore: 1
core:
  - /home/kellerb/software/root-stack/irods/plugins/auth/native/libnative.cpp:596:0
    - null pointer dereference