Fix build-binaries.sh to compile from cmd/cpm

[jeanmachuca]

What

The build-binaries.sh script uses go build . from the repo root instead of go build ./cmd/cpm. Since the main package is in cmd/cpm, this produces the wrong binary or fails to compile.

Why

• The CI in cognitiveos-distro clones cpm and runs go build . which fails with 'no Go files in ...' because the root only has library packages
• Developers building manually with build-binaries.sh get incorrect results

How

Change go build . to go build -o cpm ./cmd/cpm

[jeanmachuca]

Resolved — build-binaries.sh removed; Makefile builds from ./cmd/cpm correctly.