Replacing REDIS_STATIC with static

[ouriamzn]

As discussed, we want to remove the old REDIS_STATIC flag which is no longer relevant.

When moving from Redis to Valkey we renamed all REDIS flags in Makefile.
The REDIS_STATIC flag was renamed to SERVER_STATIC, but this change was not updated in some of the files.

After discussing it with @madolson and @ranshid, we decided that since this was introduced 10 years ago, and in many places in the code base we simply use static, we should simplify and remove the flag entirely.

[bbarani]

@ouriamzn can you please fix the DCO? It looks like the commit is incorrectly signed off.

[zuiderkwast]

As discussed

That's nothing I've heard about. Who discussed this, when and where?

[madolson]

@zuiderkwast Previous PR: #684

[ranshid]

Thank you. LGTM

I think fix the top comment so that this PR stand by itself.

[codecov]

Codecov Report

Attention: Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.

Project coverage is 70.26%. Comparing base (ce79539) to head (7072fe1).
Report is 5 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #691      +/-   ##
============================================
+ Coverage     70.05%   70.26%   +0.20%     
============================================
  Files           110      110              
  Lines         60084    60104      +20     
============================================
+ Hits          42094    42231     +137     
+ Misses        17990    17873     -117     

Files	Coverage Δ
src/quicklist.c	84.72% <93.75%> (ø)

... and 10 files with indirect coverage changes