Fix libssh2 inclusion in libgit2 iOS build script
Fix libssh2 inclusion in libgit2 iOS build script

- Added CMAKE_PREFIX_PATH to arch-specific libssh2 root dir
- Added PKG_CONFIG_USE_CMAKE_PREFIX_PATH so things actually make sense
- Removed unused LIBSSH2_INCLUDE_DIRS

blackpixel/objective-git,slavikus/objective-git,alehed/objective-git,libgit2/objective-git,nerdishbynature/objective-git,dleehr/objective-git,alehed/objective-git,dleehr/objective-git,phatblat/objective-git,nerdishbynature/objective-git,tiennou/objective-git,nerdishbynature/objective-git,tiennou/objective-git,phatblat/objective-git,dleehr/objective-git,blackpixel/objective-git,libgit2/objective-git,slavikus/objective-git,tiennou/objective-git,libgit2/objective-git,blackpixel/objective-git,dleehr/objective-git,slavikus/objective-git,alehed/objective-git,blackpixel/objective-git,libgit2/objective-git,phatblat/objective-git