[csmith-project/creduce] 745d61: Remove LLVM/Clang from Travis-CI build env.

[Eric Eide <eeide@cs.utah.edu>]

  Branch: refs/heads/master
  Home:   https://github.com/csmith-project/creduce
  Commit: 745d616f8462ae893c7d29b2c246674dd652bc3d
      https://github.com/csmith-project/creduce/commit/745d616f8462ae893c7d29b2c246674dd652bc3d
  Author: Eric Eide <eeide@cs.utah.edu>
  Date:   2016-09-12 (Mon, 12 Sep 2016)

  Changed paths:
    M scripts/travis_deps.sh

  Log Message:
  -----------
  Remove LLVM/Clang from Travis-CI build env.

The Travis-CI Ubuntu 14.04 ("trusty") build environment has LLVM and
Clang preinstalled.  They interfere with our installations of these
packages, so remove the preinstalled versions.

With the preinstalled packages in place, one gets the following error
when trying to install LLVM 3.9 in the Travis-CI "trusty" build
environment:

```
[...]
Selecting previously unselected package llvm-3.9.
Preparing to unpack .../llvm-3.9_1%3a3.9~svn279689-1~exp1_amd64.deb ...
Unpacking llvm-3.9 (1:3.9~svn279689-1~exp1) ...
dpkg: error processing archive /var/cache/apt/archives/llvm-3.9_1%3a3.9~svn279689-1~exp1_amd64.deb (--unpack):
 trying to overwrite '/usr/share/man/man1/opt.1.gz', which is also in package llvm 1:3.4-0ubuntu1
[...]
Errors were encountered while processing:
 /var/cache/apt/archives/llvm-3.9_1%3a3.9~svn279689-1~exp1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
```