Remove unnecessary intrinsics in mono/mini/intrinsics.c (#55806)

- System.Environment.IsRunningOnWindows doesn't exist in the dotnet/runtime corelib
- Microsoft.CodeAnalysis.CompilerServer.MemoryHelper.IsMemoryAvailable was used to workaround a bug that was fixed 2 years ago with dotnet/roslyn#38239 and should no longer be relevant

src/mono/mono/mini/intrinsics.c

@@ -1623,16 +1623,6 @@ mini_emit_inst_for_method (MonoCompile *cfg, MonoMethod *cmethod, MonoMethodSign
 			}
 			return ins;
 		}
-	} else if (in_corlib &&
-	        	(strcmp (cmethod_klass_name_space, "System") == 0) &&
-	        	(strcmp (cmethod_klass_name, "Environment") == 0)) {
-		if (!strcmp (cmethod->name, "get_IsRunningOnWindows") && fsig->param_count == 0) {
-#ifdef TARGET_WIN32
-			EMIT_NEW_ICONST (cfg, ins, 1);
-#else
-			EMIT_NEW_ICONST (cfg, ins, 0);
-#endif
-		}
 	} else if (in_corlib &&
 			(strcmp (cmethod_klass_name_space, "System.Reflection") == 0) &&
 			(strcmp (cmethod_klass_name, "Assembly") == 0)) {
@@ -1941,15 +1931,6 @@ mini_emit_inst_for_method (MonoCompile *cfg, MonoMethod *cmethod, MonoMethodSign
 		}
 	}
 
-	/* Workaround for the compiler server IsMemoryAvailable. */
-	if (!strcmp ("Microsoft.CodeAnalysis.CompilerServer", cmethod_klass_name_space) && !strcmp ("MemoryHelper", cmethod_klass_name)) {
-		if (!strcmp (cmethod->name, "IsMemoryAvailable")) {
-			EMIT_NEW_ICONST (cfg, ins, 1);
-			ins->type = STACK_I4;
-			return ins;
-		}
-	}
-
 	// Return false for IsSupported for all types in System.Runtime.Intrinsics.* 
 	// if it's not handled in mono_emit_simd_intrinsics
 	if (in_corlib &&