gitweb: Fix up bogus $stylesheet declarations

This seems to be a pre-++ residual declaration and it wasn't good for
anything at all besides flooding the webserver errorlog with "omg, our in
the same scope!!" warnings.

[jc: the patch was bogus by defining the variable which defeated a
 later test that checked it with "defined", which I fixed up.]

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <junkio@cox.net>

gitweb/gitweb.perl

@@ -51,12 +51,8 @@ our $site_footer = "++GITWEB_SITE_FOOTER++";
 
 # URI of stylesheets
 our @stylesheets = ("++GITWEB_CSS++");
-our $stylesheet;
-# default is not to define style sheet, but it can be overwritten later
-undef $stylesheet;
-
-# URI of default stylesheet
-our $stylesheet = "++GITWEB_CSS++";
+# URI of a single stylesheet, which can be overridden in GITWEB_CONFIG.
+our $stylesheet = undef;
 # URI of GIT logo (72x27 size)
 our $logo = "++GITWEB_LOGO++";
 # URI of GIT favicon, assumed to be image/png type