AK: Remove rsqrt()

At least on arm64, this isn't very preciese:
https://github.com/SerenityOS/serenity/issues/22739#issuecomment-1912909835

It is also now unused.

AK/Math.h

@@ -502,23 +502,6 @@ constexpr T sqrt(T x)
 #endif
 }
 
-template<FloatingPoint T>
-constexpr T rsqrt(T x)
-{
-#if ARCH(AARCH64)
-    AARCH64_INSTRUCTION(frsqrte, x);
-#elif ARCH(X86_64)
-    if constexpr (IsSame<T, float>) {
-        float res;
-        asm("rsqrtss %1, %0"
-            : "=x"(res)
-            : "x"(x));
-        return res;
-    }
-#endif
-    return (T)1. / sqrt(x);
-}
-
 template<FloatingPoint T>
 constexpr T cbrt(T x)
 {