tests: move check-misc targets from src/Makefile.am to maint.mk

tests: move check-misc targets from src/Makefile.am to maint.mk

* src/Makefile.am (check): Remove check-misc.
(check-misc): Remove target.
* maint.mk (sc_prohibit_stat_st_blocks): New target.
(sc_prohibit_S_IS_definition): New target.
* Makefile.am (EXTRA_DIST): Add .x-sc_prohibit_stat_st_blocks.
* .x-sc_prohibit_stat_st_blocks: New file.
Andreas Schwab reported that "make check" could fail to detect
violation of the no-S_IS*-definition policy.