revert zig libc implementation of pow (#31794)

Partially reverts commit b5fbed986b.

Reverts commit 7aae7dd3f4.

Closes #31207

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/31794
Co-authored-by: David Rubin <david@vortan.dev>
Co-committed-by: David Rubin <david@vortan.dev>

lib/c/math.zig

@@ -76,7 +76,6 @@ comptime {
         symbol(&modf, "modf");
         symbol(&nan, "nan");
         symbol(&nanf, "nanf");
-        symbol(&pow, "pow");
         symbol(&pow10, "pow10");
         symbol(&pow10f, "pow10f");
         symbol(&tanh, "tanh");
@@ -346,10 +345,6 @@ fn nanl(_: [*:0]const c_char) callconv(.c) c_longdouble {
     return math.nan(c_longdouble);
 }
 
-fn pow(x: f64, y: f64) callconv(.c) f64 {
-    return math.pow(f64, x, y);
-}
-
 fn pow10(x: f64) callconv(.c) f64 {
     return exp10(x);
 }