core: Remove str::init_elt

This was added based on my FIXME, but I no longer believe it has a place in
core::str, partly because it doesn't follow current naming conventions, and
partly because it can be immitated with a one liner using str::from_chars and
vec::from_elem. I have replaced the existing uses with said one-liner.

src/libcore/str.rs

@@ -20,7 +20,6 @@ export
    push_char,
    concat,
    connect,
-   init_elt,
 
    // Reinterpretation
    as_bytes,
@@ -241,16 +240,6 @@ fn connect(v: [str], sep: str) -> str {
     ret s;
 }
 
-#[doc = "Returns a string of <n_elts> repetitions of <c>, which must be \
-           UTF-8"]
-fn init_elt(n_elts: uint, c: char) -> str {
-  let mut rslt = "";
-  uint::range(0u, n_elts) {|_i|
-      push_char(rslt, c);
-  }
-  rslt
-}
-
 /*
 Section: Adding to and removing from a string
 */