tweaks: remove two unneeded unsettings

Before version 4.3, commit 3eab405e, nano would write a help text to
a temporary file and then read this file into a buffer.  The NOREAD
flag interfered with the latter, so needed to be reset for showing
help.  But since the mentioned commit nano writes a help text directly
into a buffer and the unsetting of the NOREAD flag is superfluous.

The display code never references the LINE_NUMBERS flag -- the trigger
for displaying line numbers in front of the text is 'margin > 0'.  So,
since commit 90bd25c1 that put help texts into a "normal" buffer, the
unsetting of the LINE_NUMBERS flag has been superfluous.

src/help.c

@@ -423,10 +423,8 @@ void show_help(void)
 	UNSET(USE_REGEXP);
 
 	UNSET(WHITESPACE_DISPLAY);
-	UNSET(NOREAD_MODE);
 
 #ifdef ENABLE_LINENUMBERS
-	UNSET(LINE_NUMBERS);
 	editwincols = COLS - thebar;
 	margin = 0;
 #endif