rename s/readline/get/g, and remove prefix:<=>

That's not fully correct, .get() still does unwanted context dwimmery, but
it does make three of the four failing spectests pass again.

src/classes/IO.pir

@@ -19,7 +19,7 @@ This file implements the IO file handle class.
     p6meta.'new_class'('IOIterator', 'parent'=>'Perl6Object', 'attr'=>'$!IO')
 
     $P0 = get_hll_namespace ['IO']
-    '!EXPORT'('readline', 'from'=>$P0)
+    '!EXPORT'('get', 'from'=>$P0)
 .end
 
 =head2 Methods
@@ -28,37 +28,19 @@ This file implements the IO file handle class.
 
 .namespace ['IO']
 
-=item readline
+=item get
 
 Reads a line from the file handle.
 
 =cut
 
-.sub 'readline' :method
+.sub 'get' :method
     $P0 = get_hll_global 'IOIterator'
     $P0 = $P0.'new'('IO' => self)
     .return ($P0)
 .end
 
 
-=back
-
-=head2 Functions
-
-=over 4
-
-=item C<prefix:=(IO $io)>
-
-Gets the iterator for the IO object.
-
-=cut
-
-.namespace []
-.sub 'prefix:=' :multi('IO')
-    .param pmc io
-    .tailcall io.'readline'()
-.end
-
 =back
 
 =head1 IOIterator

src/parser/grammar-oper.pg

@@ -20,7 +20,6 @@ proto prefix:<!> is equiv(prefix:<+>) { ... }
 proto prefix:<+^> is equiv(prefix:<+>)
     is pirop('bnot')
     { ... }
-proto prefix:<=> is equiv(prefix:<+>) { ... }
 proto prefix:<^> is equiv(prefix:<+>) { ... }
 proto prefix:<\> is equiv(prefix:<+>) { ... }
 proto prefix:<|> is equiv(prefix:<+>) { ... }