glew: remove glu requirement from pc file

glew adds "Requires: glu" to glew.pc, even though on fresh OS X installs
there will not be a glu.pc anywhere on the system (but the library
itself is in the system's OpenGL framework).

The requirement will actually be satisfied if XQuartz is installed, but
it's only a coincidence. So I'm removing this, which should allow gource
to build on systems without XQuartz. *shrug*

Fixes Homebrew/legacy-homebrew#22025.

Formula/glew.rb

@@ -6,6 +6,7 @@ class Glew < Formula
   sha1 'f41b45ca4a630ad1d00b8b87c5f493781a380300'
 
   def install
+    inreplace "glew.pc.in", "Requires: glu", ""
     system "make", "GLEW_DEST=#{prefix}", "all"
     system "make", "GLEW_DEST=#{prefix}", "install.all"
   end