r300: cleanup vertex program related functions

r300: cleanup vertex program related functions

- move vertex program related functions to r300_vertprog.c
- use _mesa_bitcount instead of self-made bit_count function
- remove duplicated field in r300_vertex_shader_fragment.body union
- rename r300_vertex_shader_fragment to r300_vertex_shader_hw_code
- rename r300_vertex_program field native to error
- remove unnecessary r300_vertex_shader_state structure
- remove unused r300_vertex_program and r300_vertex_program_cont fields
- remove disabled code