remove duplicate inclusion of <stdio.h> * tests/test-fprintf-posix.c: Likewise. * tests/test-printf-posix.c: Likewise. * tests/test-snprintf-posix.c: Likewise. * tests/test-sprintf-posix.c: Likewise. * tests/test-vasprintf-posix.c: Likewise. * tests/test-vfprintf-posix.c: Likewise. * tests/test-vprintf-posix.c: Likewise. * tests/test-vsnprintf-posix.c: Likewise. * tests/test-vsprintf-posix.c: Likewise.