out_file: remove workaround for Ruby 2.7 and 3.0 on macOS (fluent#4770)

**Which issue(s) this PR fixes**: 
Fixes #

**What this PR does / why we need it**: 
Next fluentd version will drop support of Ruby 3.1 or below.
Ref. fluent#4745

So, we can remove the workaround for Ruby 2.7 and 3.0 on macOS that
added at fluent#3579

**Docs Changes**:

**Release Note**:

Signed-off-by: Shizuo Fujita <[email protected]>

lib/fluent/plugin/out_file.rb

@@ -189,13 +189,6 @@ def configure(conf)
       @dir_perm = system_config.dir_permission || Fluent::DEFAULT_DIR_PERMISSION
       @file_perm = system_config.file_permission || Fluent::DEFAULT_FILE_PERMISSION
       @need_lock = system_config.workers > 1
-
-      # https://github.com/fluent/fluentd/issues/3569
-      @need_ruby_on_macos_workaround = false
-      if @append && Fluent.macos?
-        condition = Gem::Dependency.new('', [">= 2.7.0", "< 3.1.0"])
-        @need_ruby_on_macos_workaround = true if condition.match?('', RUBY_VERSION)
-      end
     end
 
     def multi_workers_ready?
@@ -244,12 +237,7 @@ def write(chunk)
 
     def write_without_compression(path, chunk)
       File.open(path, "ab", @file_perm) do |f|
-        if @need_ruby_on_macos_workaround
-          content = chunk.read()
-          f.puts content
-        else
-          chunk.write_to(f)
-        end
+        chunk.write_to(f)
       end
     end