Don't quote nil and t in doc strings

This is as per "Tips for Documentation Strings" in the elisp manual.
For consistency, do the same in diagnostics and comments.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 148d077ec21..c78d08c53d2 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -6106,7 +6106,7 @@ An entry of the form POSITION indicates that point was at the buffer
 location given by the integer.  Undoing an entry of this form places
 point at POSITION.
 
-Entries with value `nil' mark undo boundaries.  The undo command treats
+Entries with value nil mark undo boundaries.  The undo command treats
 the changes between two undo boundaries as a single step to be undone.
 
 If the value of the variable is t, undo information is not recorded.  */);