Always clean up leftovers at ci.rvm.jp

to prevent failures like
http://ci.rvm.jp/logfiles/brlog.trunk-mjit.20201126-182515.

Since fa1250a506e9b6a1bcbf664f6b7b9c06e045d9b9, it should be safe to do
this.

test/ruby/test_jit.rb

@@ -45,12 +45,10 @@ class TestJIT < Test::Unit::TestCase
     # ci.rvm.jp caches its build environment. Clean up temporary files left by SEGV.
     if ENV['RUBY_DEBUG']&.include?('ci')
       Dir.glob("#{ENV.fetch('TMPDIR', '/tmp')}/_ruby_mjit_p*u*.*").each do |file|
-        if File.mtime(file) < Time.now - 60 * 60 * 24
         puts "test/ruby/test_jit.rb: removing #{file}"
         File.unlink(file)
       end
     end
-    end
 
     # ruby -w -Itest/lib test/ruby/test_jit.rb
     if $VERBOSE