remove unnecessary quotes

Author: mohawk2

Makefile.PL

@@ -117,10 +117,10 @@ sub compileAndRun {
   my $inc = join " ", grep /^-I/, shellwords($plplot_include_path);
 
   check_lib(
-    ccflags  => "$plplot_include_path",
-    ldflags  => "$libs",
-    INC      => "$inc",
-    LIBS     => "$libs",
+    ccflags  => $plplot_include_path,
+    ldflags  => $libs,
+    INC      => $inc,
+    LIBS     => $libs,
     header   => [ 'stdio.h', $header ],
     function => $code,
     analyze_binary => sub {