move deadclass plugin to store

<sberg> noelgrandin, and is loplugin:deadclass even sound?

    struct B { B(B const &) {} }; struct D: B { D(): B(*this) {} };

Change-Id: Idadd379b925aa6f9de6c625bffa8560ec4192ac7

solenv/CompilerTest_compilerplugins_clang.mk

@@ -13,7 +13,6 @@ $(eval $(call gb_CompilerTest_add_exception_objects,compilerplugins_clang, \
     compilerplugins/clang/test/casttovoid \
     compilerplugins/clang/test/constparams \
     compilerplugins/clang/test/cppunitassertequals \
-    compilerplugins/clang/test/deadclass \
     compilerplugins/clang/test/datamembershadow \
     compilerplugins/clang/test/droplong \
     compilerplugins/clang/test/externvar \