Revert "Fix custom Eigen on macos (EIGEN_INCLUDE_DIR_HINTS)"

This reverts commit e6c5c7226d0512fd56bd79147ec745105e2f9083.

Reason for revert: <INSERT REASONING HERE>

Change-Id: I38b6a0ae0a7d835d05505d1baae33a52f4752a33

CMakeLists.txt

@@ -87,10 +87,6 @@ add_gerrit_commit_hook(${Ceres_SOURCE_DIR} ${Ceres_BINARY_DIR})
 # CMake in find_path & find_library.  This should ensure that we can
 # still build Ceres even if Homebrew is installed in a non-standard
 # location (not /usr/local).
-# Note: This is a hack that breaks HINTS passed to find_... modules
-# for thirdparty dependencies, since CMAKE_PREFIX_PATH takes
-# precendence over HINTS. See FindEigen.cmake for notes on the
-# workaround needed for making EIGEN_INCLUDE_DIR_HINTS work.
 if (CMAKE_SYSTEM_NAME MATCHES "Darwin")
   find_program(HOMEBREW_EXECUTABLE brew)
   mark_as_advanced(FORCE HOMEBREW_EXECUTABLE)

cmake/FindEigen.cmake

@@ -192,25 +192,12 @@ if (NOT EIGEN_FOUND)
     Eigen/include/eigen3 # Windows (for C:/Program Files prefix) < 3.3
     Eigen3/include/eigen3 ) # Windows (for C:/Program Files prefix) >= 3.3
 
-  # On macos with Homebrew, the brew prefix is added
-  # CMAKE_PREFIX_PATH, which overrides EIGEN_INCLUDE_DIR_HINTS in the
-  # following find_path, and the brew Eigen version is found (if
-  # installed) instead of the one provided by the hint. So, in that
-  # case we ignore CMAKE_PREFIX_PATH.  See also the comments in ceres'
-  # main CMakeLists.txt around where HOMEBREW_EXECUTABLE is set.
-  if(HOMEBREW_EXECUTABLE AND EIGEN_INCLUDE_DIR_HINTS)
-    set(FIND_PATH_FLAG NO_CMAKE_PATH)
-  else()
-    set(FIND_PATH_FLAG)
-  endif()
-
   # Search supplied hint directories first if supplied.
   find_path(EIGEN_INCLUDE_DIR
     NAMES Eigen/Core
     HINTS ${EIGEN_INCLUDE_DIR_HINTS}
     PATHS ${EIGEN_CHECK_INCLUDE_DIRS}
-    PATH_SUFFIXES ${EIGEN_CHECK_PATH_SUFFIXES}
-    ${FIND_PATH_FLAG})
+    PATH_SUFFIXES ${EIGEN_CHECK_PATH_SUFFIXES})
 
   if (NOT EIGEN_INCLUDE_DIR OR
       NOT EXISTS ${EIGEN_INCLUDE_DIR})