Remove leveldb dependency and not link it.

.travis.yml

@@ -17,8 +17,6 @@ matrix:
       osx_image: xcode9.2
 
 before_install:
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo apt-get update && sudo apt-get install libleveldb-dev; fi
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update && brew install leveldb; fi
   - git submodule update --init --recursive
 
 script:

cpp-ethereum

@@ -1 +1 @@
-Subproject commit 633c62c08bc73c7c3935c948a8d6c656a3659976
+Subproject commit c25a98257e7104875503e183dd0f27d49b3efd56