Prune unused CMake code related to external projects

CMakeLists.txt

@@ -16,31 +16,31 @@ drake_setup_platform()
 
 # eigen
 # N.B. See #5785; do your best not to have to bump this to a newer commit.
-drake_add_external(eigen CMAKE ALWAYS
+drake_add_external(eigen
   URL https://bitbucket.org/eigen/eigen/get/3.3.3.tar.gz
   URL_HASH SHA256=94878cbfa27b0d0fbc64c00d4aafa137f678d5315ae62ba4aecddbd4269ae75f
   CMAKE_ARGS
     -DEIGEN_TEST_NO_OPENGL=ON
     -DEIGEN_TEST_NOQT=ON)
 
 # fmt
-drake_add_external(fmt CMAKE ALWAYS
+drake_add_external(fmt
   URL https://github.com/fmtlib/fmt/archive/3.0.1.tar.gz
   URL_HASH SHA256=dce62ab75a161dd4353a98364feb166d35e7eea382169d59d9ce842c49c55bad
   CMAKE_ARGS
     -DFMT_DOC=OFF
     -DFMT_TEST=OFF)
 
 # gflags
-drake_add_external(gflags CMAKE ALWAYS
+drake_add_external(gflags
   URL https://github.com/gflags/gflags/archive/95ffb27c9c7496ede1409e042571054c70cb9519.tar.gz
   URL_HASH SHA256=723c21f783c720c0403c9b44bf500d1961a08bd2635cbc117107af22d2e1643f
   CMAKE_ARGS
     -DBUILD_SHARED_LIBS=ON
     -DGFLAGS_BUILD_gflags_nothreads_LIB=OFF)
 
 # nlopt
-drake_add_external(nlopt CMAKE ALWAYS
+drake_add_external(nlopt
   URL https://github.com/stevengj/nlopt/archive/45553da97c890ef58f95e7ef73c5409d2169e824.tar.gz
   URL_HASH SHA256=931fd125c50acf7cd7e709887ab4923af42a8a07be139572bf8b76bccca76450
   CMAKE_ARGS
@@ -53,7 +53,7 @@ drake_add_external(nlopt CMAKE ALWAYS
     -DUSE_SWIG=OFF)
 
 # protobuf
-drake_add_external(protobuf CMAKE ALWAYS
+drake_add_external(protobuf
   URL https://github.com/google/protobuf/archive/v3.1.0.tar.gz
   URL_HASH SHA256=fb2a314f4be897491bb2446697be693d489af645cb0e165a85e7e64e07eb134d
   SOURCE_SUBDIR cmake
@@ -63,22 +63,22 @@ drake_add_external(protobuf CMAKE ALWAYS
     -Dprotobuf_MODULE_COMPATIBLE=ON)
 
 # pybind11
-drake_add_external(pybind11 CMAKE ALWAYS
+drake_add_external(pybind11
   URL https://github.com/RobotLocomotion/pybind11/archive/6d72785766558047ee2e2075198c07d8c25eb631.tar.gz
   URL_HASH SHA256=08b4813b3b17f607efc4e8ba8b73bf55759ba744cab125e9fc666b5161cb1d0a
   CMAKE_ARGS
     -DPYBIND11_PYTHON_VERSION=${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR}
     -DPYBIND11_TEST=OFF)
 
 # tinyobjloader
-drake_add_external(tinyobjloader CMAKE ALWAYS
+drake_add_external(tinyobjloader
   URL https://github.com/syoyo/tinyobjloader/archive/v1.0.6.tar.gz
   URL_HASH SHA256=19ee82cd201761954dd833de551edb570e33b320d6027e0d91455faf7cd4c341
   CMAKE_ARGS
     -DTINYOBJLOADER_COMPILATION_SHARED=ON
   )
 
-drake_add_external(drake LOCAL CMAKE ALWAYS MATLAB PYTHON
+drake_add_external(drake LOCAL MATLAB PYTHON
   SOURCE_DIR ${PROJECT_SOURCE_DIR}/drake
   BINARY_DIR ${PROJECT_BINARY_DIR}/drake
   CMAKE_ARGS -DDISABLE_MATLAB:BOOL=${DISABLE_MATLAB}