Remove normative cites to unsafe code guidelines doc

The unsafe code guidelines document describes itself currently as
largely abandoned and indicates that those points that have found
consensus are documented in the Reference.  Let's not then normatively
cite that other document.

Let's also remove a line about "these rules do not apply..." where
"these" changed meaning when this line was copied from elsewhere.  In
the original, "these" meant rules about `readonly` and `nomem`,
whereas here, it would have seemed to refer to the rules in the UCG,
and that wouldn't make sense.

Author: traviscross

src/inline-assembly.md

@@ -1264,7 +1264,6 @@ r[asm.rules.unwind]
 
 r[asm.rules.mem-same-as-ffi]
 - The set of memory locations that assembly code is allowed to read and write are the same as those allowed for an FFI function.
-  - Refer to the unsafe code guidelines for the exact rules.
   - If the `readonly` option is set, then only memory reads are allowed.
   - If the `nomem` option is set then no reads or writes to memory are allowed.
   - These rules do not apply to memory which is private to the assembly code, such as stack space allocated within it.
@@ -1405,8 +1404,6 @@ r[asm.naked-rules.noreturn]
 
 r[asm.naked-rules.mem-same-as-ffi]
 - The set of memory locations that assembly code is allowed to read and write are the same as those allowed for an FFI function.
-  - Refer to the unsafe code guidelines for the exact rules.
-  - These rules do not apply to memory which is private to the assembly code, such as stack space allocated within the `naked_asm!` block.
 
 r[asm.naked-rules.black-box]
 - The compiler cannot assume that the instructions in the `naked_asm!` block are the ones that will actually be executed.