Revert "dump RUBY_DEBUG_LOG logs into /dev/null"

This reverts commit 8366700.

because not stable yet.

.github/workflows/compilers.yml

@@ -174,7 +174,7 @@ jobs:
 #         - { name: USE_SYMBOL_GC=0,                env: { cppflags: '-DUSE_SYMBOL_GC=0' } }
 #         - { name: USE_THREAD_CACHE=0,             env: { cppflags: '-DUSE_THREAD_CACHE=0' } }
 #         - { name: USE_TRANSIENT_HEAP=0,           env: { cppflags: '-DUSE_TRANSIENT_HEAP=0' } }
-          - { name: USE_RUBY_DEBUG_LOG=1,           env: { cppflags: '-DUSE_RUBY_DEBUG_LOG=1', RUBY_DEBUG_LOG: '/dev/null' } }
+          - { name: USE_RUBY_DEBUG_LOG=1,           env: { cppflags: '-DUSE_RUBY_DEBUG_LOG=1' } }
           - { name: USE_RVARGC=0,                   env: { cppflags: '-DUSE_RVARGC=0' } }
 #         - { name: USE_RVARGC=1,                   env: { cppflags: '-DUSE_RVARGC=1' } }
 #         - { name: USE_DEBUG_COUNTER,              env: { cppflags: '-DUSE_DEBUG_COUNTER=1', RUBY_DEBUG_COUNTER_DISABLE: '1' } }