kconfig: stop supporting '.' and '/' in unquoted words

In my understanding, special characters such as '.' and '/' are
supported in unquoted words to use bare file paths in the "source"
statement.

With the previous commit surrounding all file paths with double
quotes, we can drop this.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/kconfig/preprocess.c

@@ -555,8 +555,7 @@ char *expand_string(const char *in)
 
 static bool is_end_of_token(char c)
 {
-	/* Why are '.' and '/' valid characters for symbols? */
-	return !(isalnum(c) || c == '_' || c == '-' || c == '.' || c == '/');
+	return !(isalnum(c) || c == '_' || c == '-');
 }
 
 /*