Remove redundant code from PHP workflows

[prateek-kumar-improving]

Clean up redundant .submodule-commits generation and head -1 guards

Problem:

• publish-pecl.yml generates .submodule-commits before calling build-pecl-package/action.yml, which immediately truncates and regenerates the same file.
• config.m4 and Makefile.frag contain head -1 guards to protect against duplicate entries in .submodule-commits, but the truncation (>) in build-pecl-package already prevents duplicates from ever occurring.

Changes needed:

1. .github/workflows/publish-pecl.yml — Remove the "Generate submodule commit info" step since build-pecl-package/action.yml already handles this independently.
2. config.m4 — Remove | head -1 from the line reading .submodule-commits.
3. Makefile.frag — Remove | head -1 from the line reading .submodule-commits.