configure: do not blank $LIBNAME if static libs disabled

Whatever reason this was done for no longer applies, and it causes
lots of make warnings.
Signed-off-by: NMans Rullgard <mans@mansr.com>

configure

@@ -2524,8 +2524,6 @@ EOF
     exit 1;
 fi
 
-disabled static && LIBNAME=""
-
 die_license_disabled() {
     enabled $1 || { enabled $2 && die "$2 is $1 and --enable-$1 is not specified."; }
 }