android: fix build by removing references to dri-search-path

In commit 41e83b243c (meson: remove dri-search-path, 2024-09-18) the
`dri-search-path` meson option was removed but its usage in the Android
build files was left there, resulting in the following error when
building for Android:

-----------------------------------------------------------------------
FAILED: out/target/product/vsoc_x86_64/obj_x86/MESON_MESA3D/.build.timestamp
...

meson.build:4:0: ERROR: Unknown options: "dri-search-path"
-----------------------------------------------------------------------

Remove the usage of the option when building for Android, and while at
it remove also any mention of if in docs/drivers/llvmpipe.rst

Remove also the MESA3D_LIB_DIR variable which was used only for
dri-search-path.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31266>

android/mesa3d_cross.mk

@@ -57,8 +57,6 @@ link_deps := \
 # Build mesa3d using intermediate variables provided by AOSP make/core internals
 M_TARGET_PREFIX := $(my_2nd_arch_prefix)
 
-MESA3D_LIB_DIR := lib$(subst 32,,$(LOCAL_MULTILIB))
-
 MESON_OUT_DIR                            := $($(M_TARGET_PREFIX)TARGET_OUT_INTERMEDIATES)/MESON_MESA3D
 MESON_GEN_DIR                            := $(MESON_OUT_DIR)_GEN
 MESON_GEN_FILES_TARGET                   := $(MESON_GEN_DIR)/.timestamp
@@ -83,7 +81,6 @@ MESON_GEN_NINJA := \
 	cd $(MESON_OUT_DIR) && PATH=/usr/bin:/usr/local/bin:$$PATH meson ./build     \
 	--cross-file $(call relative-to-absolute,$(MESON_GEN_DIR))/aosp_cross        \
 	--buildtype=release                                                          \
-	-Ddri-search-path=/vendor/$(MESA3D_LIB_DIR)/dri                              \
 	-Dplatforms=android                                                          \
 	-Dplatform-sdk-version=$(PLATFORM_SDK_VERSION)                               \
 	-Dgallium-drivers=$(subst $(space),$(comma),$(BOARD_MESA3D_GALLIUM_DRIVERS)) \