Remove absolute path from libpython.dylib (#2256)

Previously this set the install name of the binary, which is put into
any binaries that link this, as an absolute path that is user specific.
Instead this can be fetched relatively, and bazel will automatically
handle adding the correct rpaths for this.

python/private/python_repository.bzl

@@ -143,12 +143,11 @@ def _python_repository_impl(rctx):
         # dyld lookup errors. To fix, set the full path to the dylib as
         # it appears in the Bazel workspace as its LC_ID_DYLIB using
         # the `install_name_tool` bundled with macOS.
-        dylib = "lib/libpython{}.dylib".format(python_short_version)
-        full_dylib_path = rctx.path(dylib)
+        dylib = "libpython{}.dylib".format(python_short_version)
         repo_utils.execute_checked(
             rctx,
             op = "python_repository.FixUpDyldIdPath",
-            arguments = [repo_utils.which_checked(rctx, "install_name_tool"), "-id", full_dylib_path, dylib],
+            arguments = [repo_utils.which_checked(rctx, "install_name_tool"), "-id", "@rpath/{}".format(dylib), "lib/{}".format(dylib)],
             logger = logger,
         )