Refactoring based on suggestions

Defaulting zip_dep_if_needed(tags) and bzip2_dep_if_needed(tags)
methods to those on Linux and overriding them on macOS.

Library/Homebrew/dependency_collector.rb

@@ -72,9 +72,13 @@ class DependencyCollector
 
   def ld64_dep_if_needed(*); end
 
-  def zip_dep_if_needed(*); end
+  def zip_dep_if_needed(tags)
+    Dependency.new("zip", tags)
+  end
 
-  def bzip2_dep_if_needed(*); end
+  def bzip2_dep_if_needed(tags)
+    Dependency.new("bzip2", tags)
+  end
 
   def self.tar_needs_xz_dependency?
     !new.xz_dep_if_needed([]).nil?

Library/Homebrew/extend/os/dependency_collector.rb

@@ -1,3 +1,2 @@
 require "dependency_collector"
 require "extend/os/mac/dependency_collector" if OS.mac?
-require "extend/os/linux/dependency_collector" if OS.linux?

Library/Homebrew/extend/os/linux/dependency_collector.rb

@@ -1,23 +0,0 @@
-class DependencyCollector
-  def git_dep_if_needed(tags)
-    Dependency.new("git", tags)
-  end
-
-  def cvs_dep_if_needed(tags)
-    Dependency.new("cvs", tags)
-  end
-
-  def xz_dep_if_needed(tags)
-    Dependency.new("xz", tags)
-  end
-
-  def ld64_dep_if_needed(*); end
-
-  def zip_dep_if_needed(tags)
-    Dependency.new("zip", tags)
-  end
-
-  def bzip2_dep_if_needed(tags)
-    Dependency.new("bzip2", tags)
-  end
-end