date.c: make parse_date_basic() file-scope static

When we dropped vcs-svn experiment at fc47391 (drop vcs-svn
experiment, 2020-08-13), we lost the last and the only caller
of parse_date_basic().

We still internally make calls to it as we have always done.  Make
it file-scope static.

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

date.c

@@ -874,7 +874,7 @@ static const timestamp_t timestamp_max = (((timestamp_t)2100 - 1970) * 365 + 32)
 
 /* Gr. strptime is crap for this; it doesn't have a way to require RFC2822
    (i.e. English) day/month names, and it doesn't work correctly with %z. */
-int parse_date_basic(const char *date, timestamp_t *timestamp, int *offset)
+static int parse_date_basic(const char *date, timestamp_t *timestamp, int *offset)
 {
 	struct tm tm;
 	int tm_gmt;

date.h

@@ -63,7 +63,6 @@ void date_mode_release(struct date_mode *mode);
 
 void show_date_relative(timestamp_t time, struct strbuf *timebuf);
 int parse_date(const char *date, struct strbuf *out);
-int parse_date_basic(const char *date, timestamp_t *timestamp, int *offset);
 int parse_expiry_date(const char *date, timestamp_t *timestamp);
 void datestamp(struct strbuf *out);
 #define approxidate(s) approxidate_careful((s), NULL)