Remove stale code, delete alert_tests.cpp

Author: laanwj

src/Makefile.test.include

@@ -28,7 +28,6 @@ BITCOIN_TESTS =\
   test/arith_uint256_tests.cpp \
   test/scriptnum10.h \
   test/addrman_tests.cpp \
-  test/alert_tests.cpp \
   test/amount_tests.cpp \
   test/allocator_tests.cpp \
   test/base32_tests.cpp \