Revert "lib: newlib: Add workaround for #38258"

The commit 9bd1483afeb18f4225ec7b0340b0d4e20efb7d01 was added as a
workaround for the Xtensa initial malloc failure bug.

This bug has been fixed in the Zephyr SDK 0.13.1 release and therefore
this workaround is no longer needed.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

lib/libc/newlib/libc-hooks.c

@@ -130,20 +130,6 @@ static int malloc_prepare(const struct device *unused)
 		 "minimum required size specified by "
 		 "CONFIG_NEWLIB_LIBC_MIN_REQUIRED_HEAP_SIZE");
 
-#ifdef CONFIG_XTENSA
-	/*
-	 * FIXME: For Xtensa, the first `malloc` call may fail if the HEAP_BASE
-	 *        is such that the first `sbrk` call returns a 4096-byte
-	 *        aligned address.
-	 *
-	 *        This is a very ugly workaround for the issue #38258 and must
-	 *        be removed once it is fixed.
-	 */
-	void *ptr = malloc(16);
-
-	free(ptr);
-#endif /* CONFIG_XTENSA */
-
 	return 0;
 }