Kill off has-accessor.

MOP objects consistently use _ rather than - in their names, and
Attribute is decidedly MOP. Further, every other method on it uses
the _ convention, and we still had has_accessor anyway.

src/Perl6/Metamodel/BOOTSTRAP.nqp

@@ -28,7 +28,6 @@ my class BOOTSTRAPATTR {
     method package() { $!package }
     method inlined() { $!inlined }
     method has_accessor() { 0 }
-    method has-accessor() { 0 }
     method positional_delegate() { 0 }
     method associative_delegate() { 0 }
     method build() { }

src/core/Attribute.pm

@@ -110,7 +110,6 @@ my class Attribute { # declared in BOOTSTRAP
     }
 
     method container() is raw { nqp::isnull($!auto_viv_container) ?? Nil !! $!auto_viv_container }
-    method has-accessor() { ?$!has_accessor }
     method readonly() { !self.rw }
     method package() { $!package }
     method inlined() { $!inlined }

src/core/Mu.pm

@@ -505,7 +505,7 @@ Please refactor this code using the new Iterator / Seq interface.
                 my $acc_name := substr($name,2);
                 nqp::getattr($cloned, $package, $name) =
                   nqp::decont(%twiddles{$acc_name})
-                  if $attr.has-accessor && %twiddles.EXISTS-KEY($acc_name);
+                  if $attr.has_accessor && %twiddles.EXISTS-KEY($acc_name);
             }
         }
         else {
@@ -526,7 +526,7 @@ Please refactor this code using the new Iterator / Seq interface.
     method Capture() {
         my %attrs;
         for self.^attributes.flat -> $attr {
-            if $attr.has-accessor {
+            if $attr.has_accessor {
                 my $name = substr($attr.name,2);
                 unless %attrs.EXISTS-KEY($name) {
                     %attrs{$name} = self."$name"();