Cleanup error messages, improve docstrings

src/test/ui/parser/raw/raw-byte-string-eof.stderr

@@ -2,7 +2,7 @@ error[E0748]: unterminated raw string
   --> $DIR/raw-byte-string-eof.rs:2:5
    |
 LL |     br##"a"#;
-   |     ^      - help: you might have intended to terminate the string here: `##`
+   |     ^      - help: consider terminating the string here: `##`
    |     |
    |     unterminated raw string
    |

src/test/ui/parser/raw/raw-str-unbalanced.stderr

@@ -2,9 +2,9 @@ error: too many `#` when terminating raw string
   --> $DIR/raw-str-unbalanced.rs:3:9
    |
 LL |       "##
-   |         ^ help: Remove the extra `#`
+   |         ^ help: remove the extra `#`
    |
-   = note: The raw string started with 1 `#`s
+   = note: the raw string started with 1 `#`s
 
 error: aborting due to previous error
 

src/test/ui/parser/raw/raw_string.stderr

@@ -2,7 +2,7 @@ error[E0748]: unterminated raw string
   --> $DIR/raw_string.rs:2:13
    |
 LL |     let x = r##"lol"#;
-   |             ^       - help: you might have intended to terminate the string here: `##`
+   |             ^       - help: consider terminating the string here: `##`
    |             |
    |             unterminated raw string
    |