move g_test_dbg_lock_sleep from a global to a function level static

This avoids the need to define that variable in every program
which uses epee.

src/miner/simpleminer.cpp

@@ -41,7 +41,6 @@
 
 using namespace epee;
 namespace po = boost::program_options;
-unsigned int epee::g_test_dbg_lock_sleep = 0;
 
 int main(int argc, char** argv)
 {