Remove compat snprintf() (eggdrop requires posix 2001)

[michaelortmann]

Found by: vanosg
Patch by: michaelortmann
Fixes:

One-line summary:
Eggdrop depends on POSIX.1-2001, which defines vsnprintf().

Additional description (if needed):
This PR keeps egg_snprintf() for backward compatibility to (older) modules but redefines it to use snprintf() directly with a one-liner define in eggdrop.h.

All egg_snprintf() were replaced by snprintf():
find ./ -type f -exec sed -i 's/egg_snprintf(/snprintf(/g' {} \;
Note: don't do this in git directory. cd src/ first!

This PR will lead to better compiler diagnostics, new warnings during make, and codacy static code analysis findings, as expected. Follow-UP PRs should fix them to keep this very PR small and thus easier to review.

Test cases demonstrating functionality (if applicable):
No functional change. I tested 2 share bots, which successfully started and shared userfile.

[michaelortmann]

This PR leads to better diagnostics / more compiler warnings. Now i fixed some of those, the easy to fix ones. The remaining ones are also easy to fix but will need more changes / code lines, so i leave those to a Follow-up PR to help the review-process.