[Hexagon] Update hexagon API build instruction and cleanup hexagon_proxy_rpc (#10068)

* Fix hexagon api build and Update Readme

* Cleanup hexagon_proxy_rpc

* Target Hack

* Remove hack

* address @cconvey comments

* remove the rest of proxy rpc

Author: mehrdadh

apps/hexagon_api/CMakeLists.txt

@@ -88,3 +88,5 @@ ExternalProject_Add_Step(hexagon_tvm_runtime_rpc copy_binaries
   DEPENDEES install
 )
 
+configure_file("${TVM_SOURCE_DIR}/src/runtime/hexagon/rpc/android_bash.sh.template"
+  ${HEXAGON_API_BINARY_DIR} COPYONLY)