Remove noise() from core library (#6421)

noise() is currently marked "unsupported" in Slang documentation, and
has also been unsupported in HLSL since SM 2.0

Until now, noise() was present only to prevent compilation errors, but
not for any actual use since it returns 0.0 always.

Closes #5775

Author: cheneym2

source/slang/hlsl.meta.slang

@@ -11676,25 +11676,6 @@ vector<T,N> nextafter(vector<T,N> x, vector<T,N> y)
     }
 }
 
-/// Generate a random number (unsupported).
-/// @param x The seed value.
-/// @remarks This function is not supported in that it always returns 0.
-/// @deprecated
-/// @category math
-[__readNone]
-[deprecated("Always returns 0")]
-float noise(float x)
-{
-    return 0;
-}
-
-[__readNone]
-[deprecated("Always returns 0")]
-__generic<let N : int> float noise(vector<float, N> x)
-{
-    return 0;
-}
-
 /// Indicate that an index may be non-uniform at execution time.
 ///
 /// Shader Model 5.1 and 6.x introduce support for dynamic indexing