Back out the structure literal syntax separation.

It breaks syntax highlighting for string interpolation, and I spent like
2 hours trying to figure out why adding `leanStringInterpolation` to the
`containedin=ALLBUT` doesn't fix it, but it doesn't.

We don't need this anymore for indent, so, go away.

syntax/lean.vim

@@ -66,9 +66,9 @@ syn region leanEncl matchgroup=leanDelim start="#\[" end="\]" contains=TOP conta
 syn region leanEncl matchgroup=leanDelim start="(" end=")" contains=TOP containedin=ALLBUT,leanBlockComment,leanComment,leanFrenchQuote keepend
 syn region leanEncl matchgroup=leanDelim start="\[" end="\]" contains=TOP containedin=ALLBUT,leanBlockComment,leanComment,leanFrenchQuote keepend
 syn region leanEncl matchgroup=leanDelim start="⦃"  end="⦄" contains=TOP containedin=ALLBUT,leanBlockComment,leanComment,leanFrenchQuote keepend
+syn region leanEncl matchgroup=leanDelim start="⟨"  end="⟩" contains=TOP containedin=ALLBUT,leanBlockComment,leanComment,leanFrenchQuote keepend
 
 syn region leanAnonymousLiteral matchgroup=leanDelim start="⟨"  end="⟩" contains=TOP containedin=ALLBUT,leanBlockComment,leanComment,leanFrenchQuote keepend
-syn region leanStructureLiteral matchgroup=leanDelim start="{"  end="}" contains=TOP containedin=ALLBUT,leanBlockComment,leanComment,leanFrenchQuote keepend
 
 " FIXME(gabriel): distinguish backquotes in notations from names
 " syn region      leanNotation        start=+`+    end=+`+