Revert "Preserve the directory structure under tool/ruby_vm/views"

This reverts commit 62ec621f8c.

will revisit this once fixing non-MJIT targets

template/Makefile.in

@@ -505,7 +505,7 @@ clean-local::
 	-$(Q) $(RMDIRS) $(MJIT_HEADER_INSTALL_DIR) $(MJIT_HEADER_BUILD_DIR) $(TIMESTAMPDIR) 2> $(NULL) || $(NULLCMD)
 
 main: $(srcdir)/lib/mjit/instruction.rb
-$(srcdir)/lib/mjit/instruction.rb: $(tooldir)/ruby_vm/views/lib/mjit/instruction.rb.erb $(srcdir)/insns.def
+$(srcdir)/lib/mjit/instruction.rb: $(tooldir)/ruby_vm/views/instruction.rb.erb $(srcdir)/insns.def
 	$(ECHO) generating $@
 	$(Q) $(BASERUBY) -Ku $(tooldir)/insns2vm.rb $(INSNS2VMOPT) $@
 

tool/ruby_vm/helpers/dumper.rb

@@ -25,11 +25,10 @@ class RubyVM::Dumper
   end
 
   def new_erb spec
-    srcdir = Pathname.new(__dir__).parent.parent.parent
     path  = Pathname.new(__FILE__)
     path  = (path.relative_path_from(Pathname.pwd) rescue path).dirname
     path += '../views'
-    path += Pathname.pwd.join(spec).to_s.sub("#{srcdir}/", '')
+    path += File.basename(spec)
     src   = path.read mode: 'rt:utf-8:utf-8'
   rescue Errno::ENOENT
     raise "don't know how to generate #{path}"