Delete unused requirements file, simplify nanobind build file (#1635)

The dependencies are contained in the `pyproject.toml` since it was added.

Switches to header and source file globbing instead of manually listing
the files. The selects for different platforms are removed, as a tradeoff,
we take a single- to low double-digit hit in wheel sizes (between 5 percent
zipped and 12% installed on MacOS 13.4).

bindings/python/nanobind.BUILD

@@ -1,57 +1,17 @@
-
-config_setting(
-    name = "msvc_compiler",
-    flag_values = {"@bazel_tools//tools/cpp:compiler": "msvc-cl"},
-)
-
 cc_library(
     name = "nanobind",
-    hdrs = glob(
-        include = [
-            "include/nanobind/*.h",
-            "include/nanobind/stl/*.h",
-            "include/nanobind/detail/*.h",
-        ],
-        exclude = [],
-    ),
-    srcs = [
-        "include/nanobind/stl/detail/nb_dict.h",
-        "include/nanobind/stl/detail/nb_list.h",
-        "include/nanobind/stl/detail/traits.h",
-        "ext/robin_map/include/tsl/robin_map.h",
-        "ext/robin_map/include/tsl/robin_hash.h",
-        "ext/robin_map/include/tsl/robin_growth_policy.h",
-        "ext/robin_map/include/tsl/robin_set.h",
-        "src/buffer.h",
-        "src/common.cpp",
-        "src/error.cpp",
-        "src/implicit.cpp",
-        "src/nb_enum.cpp",
-        "src/nb_func.cpp",
-        "src/nb_internals.cpp",
-        "src/nb_internals.h",
-        "src/nb_ndarray.cpp",
-        "src/nb_static_property.cpp",
-        "src/nb_type.cpp",
-        "src/trampoline.cpp",
-    ],
-    copts = select({
-        ":msvc_compiler": [],
-        "//conditions:default": [
-        "-fexceptions",
-        "-Os",  # size optimization
-        "-flto", # enable LTO
-        ],
-    }),
-    linkopts = select({
-        "@com_github_google_benchmark//:macos": [
-        "-undefined dynamic_lookup",
-        "-Wl,-no_fixup_chains",
-        "-Wl,-dead_strip",
-        ],
-        "//conditions:default": [],
-    }),
+    srcs = glob([
+        "src/*.cpp"
+    ]),
+    copts = ["-fexceptions"],
     includes = ["include", "ext/robin_map/include"],
+    textual_hdrs = glob(
+        [
+            "include/**/*.h",
+            "src/*.h",
+            "ext/robin_map/include/tsl/*.h",
+        ],
+    ),
     deps = ["@python_headers"],
     visibility = ["//visibility:public"],
 )

bindings/python/requirements.txt

@@ -1,2 +0,0 @@
-absl-py>=0.7.1
-