Convert phase to htslib API

Convert samtools phase command to use new htslib API.
Remove bam1_dup from bam.h to make room for htslib bam1_dup.

Signed-off-by: Martin O. Pollard <mp15@sanger.ac.uk>
bam_dup1() is now provided by htslib

As of samtools/htslib@cd410e1cf9a3d422f990a34caa10e63bfecfd5e5 this
function is provided by <htslib/sam.h>, which this header #includes.
Merge phase.c htslibification (PR #190)