lex: remove ** operator

I don't think this would be useful, and it would
only complicate parsing due to its right
associativity, so it has to go

operator-precedence.txt

@@ -9,7 +9,6 @@ L2R:  &
 L2R:  <<  >>
 L2R:  +  - (binary minus)
 L2R:  *  /  %
-L2R:  **
 R2L:  !  - (unary minus)
 L2R:  ()  []  .
 

src/lex/mod.rs

@@ -100,8 +100,6 @@ impl Iterator for Lexer {
             '+' => self.token_ok(token::Kind::Plus),
             '-' if self.skip_if_match("=") => self.token_ok(token::Kind::MinusEq),
             '-' => self.token_ok(token::Kind::Minus),
-            '*' if self.skip_if_match("*=") => self.token_ok(token::Kind::AsteriskAsteriskEq),
-            '*' if self.skip_if_match("*") => self.token_ok(token::Kind::AsteriskAsterisk),
             '*' if self.skip_if_match("=") => self.token_ok(token::Kind::AsteriskEq),
             '*' => self.token_ok(token::Kind::Asterisk),
             '/' if self.skip_if_match("=") => self.token_ok(token::Kind::SlashEq),

src/lex/token.rs

@@ -62,9 +62,7 @@ pub enum Kind {
     Minus,
     MinusEq,
     Asterisk,
-    AsteriskAsterisk,
     AsteriskEq,
-    AsteriskAsteriskEq,
     Slash,
     SlashEq,
     Percent,
@@ -110,7 +108,6 @@ impl Kind {
             Kind::PlusEq => true,
             Kind::MinusEq => true,
             Kind::AsteriskEq => true,
-            Kind::AsteriskAsteriskEq => true,
             Kind::SlashEq => true,
             Kind::PercentEq => true,
             Kind::GtGtEq => true,
@@ -130,7 +127,6 @@ impl Kind {
             Kind::PlusEq => Some(2),
             Kind::MinusEq => Some(2),
             Kind::AsteriskEq => Some(2),
-            Kind::AsteriskAsteriskEq => Some(2),
             Kind::SlashEq => Some(2),
             Kind::PercentEq => Some(2),
             Kind::AmpEq => Some(2),
@@ -156,7 +152,6 @@ impl Kind {
             Kind::Asterisk => Some(11),
             Kind::Slash => Some(11),
             Kind::Percent => Some(11),
-            Kind::AsteriskAsterisk => Some(12),
             _ => None,
         }
     }
@@ -206,9 +201,7 @@ impl fmt::Display for Kind {
                 Kind::Minus => "minus",
                 Kind::MinusEq => "minuseq",
                 Kind::Asterisk => "asterisk",
-                Kind::AsteriskAsterisk => "asteriskasterisk",
                 Kind::AsteriskEq => "asteriskeq",
-                Kind::AsteriskAsteriskEq => "asteriskasteriskeq",
                 Kind::Slash => "slash",
                 Kind::SlashEq => "slasheq",
                 Kind::Percent => "percent",