tweak wording

Author: RalfJung

src/stacked_borrows/diagnostics.rs

@@ -363,7 +363,7 @@ impl<'span, 'history, 'ecx, 'mir, 'tcx> DiagnosticCx<'span, 'history, 'ecx, 'mir
                 [
                     (
                         format!(
-                            "{tag:?} cannot be activated because of protected derived tag {protected_tag:?} which was created here"
+                            "{tag:?} cannot be used for memory access because that would remove protected tag {protected_tag:?}, created here"
                         ),
                         protected_tag_span,
                     ),

tests/fail/stacked_borrows/aliasing_mut1.stderr

@@ -11,7 +11,7 @@ help: <TAG> was created by a Unique retag at offsets [0x0..0x4]
    |
 LL |     let xraw: *mut i32 = unsafe { mem::transmute(&mut x) };
    |                                                  ^^^^^^
-help: <TAG> cannot be activated because of protected derived tag <TAG> which was created here
+help: <TAG> cannot be used for memory access because that would remove protected tag <TAG>, created here
   --> $DIR/aliasing_mut1.rs:LL:CC
    |
 LL |     let xraw: *mut i32 = unsafe { mem::transmute(&mut x) };

tests/fail/stacked_borrows/aliasing_mut2.stderr

@@ -11,7 +11,7 @@ help: <TAG> was created by a Unique retag at offsets [0x0..0x4]
    |
 LL |     let xref = &mut x;
    |                ^^^^^^
-help: <TAG> cannot be activated because of protected derived tag <TAG> which was created here
+help: <TAG> cannot be used for memory access because that would remove protected tag <TAG>, created here
   --> $DIR/aliasing_mut2.rs:LL:CC
    |
 LL |     safe_raw(xshr, xraw);

tests/fail/stacked_borrows/aliasing_mut4.stderr

@@ -11,7 +11,7 @@ help: <TAG> was created by a Unique retag at offsets [0x0..0x4]
    |
 LL |     let xref = &mut x;
    |                ^^^^^^
-help: <TAG> cannot be activated because of protected derived tag <TAG> which was created here
+help: <TAG> cannot be used for memory access because that would remove protected tag <TAG>, created here
   --> $DIR/aliasing_mut4.rs:LL:CC
    |
 LL |     safe_raw(xshr, xraw as *mut _);

tests/fail/stacked_borrows/illegal_write6.stderr

@@ -11,7 +11,7 @@ help: <TAG> was created by a SharedReadWrite retag at offsets [0x0..0x4]
    |
 LL |     let p = x as *mut u32;
    |             ^
-help: <TAG> cannot be activated because of protected derived tag <TAG> which was created here
+help: <TAG> cannot be used for memory access because that would remove protected tag <TAG>, created here
   --> $DIR/illegal_write6.rs:LL:CC
    |
 LL |     foo(x, p);

tests/fail/stacked_borrows/invalidate_against_barrier1.stderr

@@ -11,7 +11,7 @@ help: <TAG> was created by a SharedReadWrite retag at offsets [0x0..0x4]
    |
 LL |     let xraw = &mut x as *mut _;
    |                ^^^^^^
-help: <TAG> cannot be activated because of protected derived tag <TAG> which was created here
+help: <TAG> cannot be used for memory access because that would remove protected tag <TAG>, created here
   --> $DIR/invalidate_against_barrier1.rs:LL:CC
    |
 LL |     inner(xraw, xref);

tests/fail/stacked_borrows/invalidate_against_barrier2.stderr

@@ -11,7 +11,7 @@ help: <TAG> was created by a SharedReadWrite retag at offsets [0x0..0x4]
    |
 LL |     let xraw = &mut x as *mut _;
    |                ^^^^^^
-help: <TAG> cannot be activated because of protected derived tag <TAG> which was created here
+help: <TAG> cannot be used for memory access because that would remove protected tag <TAG>, created here
   --> $DIR/invalidate_against_barrier2.rs:LL:CC
    |
 LL |     inner(xraw, xref);

tests/fail/stacked_borrows/newtype_retagging.stderr

@@ -11,7 +11,7 @@ help: <TAG> was created by a SharedReadWrite retag at offsets [0x0..0x4]
    |
 LL |     let ptr = Box::into_raw(Box::new(0i32));
    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-help: <TAG> cannot be activated because of protected derived tag <TAG> which was created here
+help: <TAG> cannot be used for memory access because that would remove protected tag <TAG>, created here
   --> $DIR/newtype_retagging.rs:LL:CC
    |
 LL |             Newtype(&mut *ptr),