mingw: do not special-case .exe files anymore

Since baaf233 (connect: improve check for plink to reduce false
positives, 2015-04-26), t5601 writes out a `plink.exe` for testing that
is actually a shell script. So the assumption that the `.exe` extension
implies that the file is *not* a shell script is now wrong.

The original idea to special-case `.exe` files was probably to
help performance, but since we are in a code path that involves spawning
a new process (which in and of itself is pretty slow on Windows anyway),
we pursue a better idea to improve performance elsewhere: we try to
convert scripts into builtins and to reduce the number of spawned
processes by adding more internal API calls.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

compat/mingw.c

@@ -836,11 +836,6 @@ static const char *parse_interpreter(const char *cmd)
 	char *p, *opt;
 	int n, fd;
 
-	/* don't even try a .exe */
-	n = strlen(cmd);
-	if (n >= 4 && !strcasecmp(cmd+n-4, ".exe"))
-		return NULL;
-
 	fd = open(cmd, O_RDONLY);
 	if (fd < 0)
 		return NULL;