Revert "Add flags to build prometheus statically"

This reverts commit 0e9e3e068d7e164a0069240cf54cbddc53abbe22.

Not only do we know this to produce problematic artifacts, it refuses
to build on Mac OS X.

    TMPDIR=/tmp GOROOT=/Users/mattproud/Development/go/src/github.com/prometheus/prometheus/.build/root/go GOPATH=/Users/mattproud/Development/go/src/github.com/prometheus/prometheus/.build/root/gopath /Users/mattproud/Development/go/src/github.com/prometheus/prometheus/.build/root/go/bin/go build -o prometheus -ldflags " -X main.buildVersion c7052ed -X main.buildBranch refactor/storage/modify-append-signature -X main.buildUser mattproud@Berlin.local -X main.buildDate 20130815-11:15:49 -X main.goVersion 1.1 -X main.leveldbVersion 1.12.0 -X main.protobufVersion 2.5.0 -X main.snappyVersion 1.1.0 -linkmode external -extldflags '-lstdc++ -lpthread -static /Users/mattproud/Development/go/src/github.com/prometheus/prometheus/.build/root/lib/libleveldb.a /Users/mattproud/Development/go/src/github.com/prometheus/prometheus/.build/root/lib/libsnappy.a'" .
    # _/Users/mattproud/Development/go/src/github.com/prometheus/prometheus
    ld: library not found for -lcrt0.o

Change-Id: I4f42161aebfd35a6f09cd7f984b78cc4498774aa