Remove duplicate definition of PAPI_num_hwctrs.
Remove duplicate definition of PAPI_num_hwctrs.

In the merge of papi-c-exp in 2009 a second prototype for
PAPI_num_hwctrs included, see 7bcc8f01 for details.

arm-hpc/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi