travis-ci: don't build Git for the static analysis job

The static analysis job on Travis CI builds Git ever since it was introduced in d8245bb3f (travis-ci: add static analysis build job to run coccicheck, 2017-04-11). However, Coccinelle, the only static analysis tool in use, only needs Git's source code to work and it doesn't care about built Git binaries at all.

Spare some of Travis CI's resources and don't build Git for the static analysis job unnecessarily.

---
 .travis.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index fead995ed..281f101f3 100644
@@ -71,7 +71,7 @@ matrix:
           packages:
           - coccinelle
       before_install:
-      # "before_script" that builds Git is inherited from base job
+      before_script:
       script: ci/run-static-analysis.sh
       after_failure:
     - env: Documentation

2.15.0.67.gb67a46776