configure: Don't disable optimizations when enabling debug

Optimization is now on by default. Closes rust-lang#24405

Author: richo

configure

@@ -633,8 +633,6 @@ esac
 # Adjust perf and debug options for debug mode
 if [ -n "$CFG_ENABLE_DEBUG" ]; then
     msg "debug mode enabled, setting performance options"
-    CFG_DISABLE_OPTIMIZE=1
-    CFG_DISABLE_OPTIMIZE_CXX=1
     CFG_ENABLE_LLVM_ASSERTIONS=1
     CFG_ENABLE_DEBUG_ASSERTIONS=1
     CFG_ENABLE_DEBUG_JEMALLOC=1