Fixed the stray On-block reference

Author: Lut99

specification/src/appendix/languages/bscript/syntax.md

@@ -73,9 +73,7 @@ Parallel ::= PARALLEL LBRACKET PBlocks RBRACKET SEMICOLON
            | LET IDENT ASSIGN PARALLEL LBRACKET PBlocks RBRACKET SEMICOLON
            | LET IDENT ASSIGN PARALLEL LBRACKET IDENT RBRACKET LBRACKET PBlocks RBRACKET SEMICOLON
  PBlocks ::= PBlocks COMMA Block
-           | PBlocks COMMA On
            | Block
-           | On
 
 Return ::= RETURN Expr SEMICOLON
          | RETURN SEMICOLON