Revert (some) const functionality from #296

[clubby789]

While marking functions as const in the PR (#296), I didn't notice a few issues, such as

iced/src/rust/iced-x86/src/decoder.rs

Lines 1247 to 1251 in 84fa85b

	#[must_use]
	#[inline]
	pub const fn can_decode(&self) -> bool {
	self.data_ptr != self.data_ptr_end
	}

Comparing pointers in a const context is disallowed without unstable features, but since the pointers are stored as usize, rustc didn't warn of the issue.

There might be other functions that shouldn't be const, this is just the first one I noticed.

[wtfsck]

There are only 6 const fn in that file, so seems like you found the only function that shouldn't be const. Want to send a PR?