[libc] Use generic 'atan2' function for the GPU

Summary:
I forget to enable this one in the previous patch.

Author: jhuber6

libc/src/math/amdgpu/CMakeLists.txt

@@ -408,18 +408,6 @@ add_entrypoint_object(
   VENDOR
 )
 
-add_entrypoint_object(
-  atan2
-  SRCS
-    atan2.cpp
-  HDRS
-    ../atan2.h
-  COMPILE_OPTIONS
-    ${bitcode_link_flags}
-    -O2
-  VENDOR
-)
-
 add_entrypoint_object(
   atanh
   SRCS

libc/src/math/nvptx/CMakeLists.txt

@@ -349,18 +349,6 @@ add_entrypoint_object(
   VENDOR
 )
 
-add_entrypoint_object(
-  atan2
-  SRCS
-    atan2.cpp
-  HDRS
-    ../atan2.h
-  COMPILE_OPTIONS
-    ${bitcode_link_flags}
-    -O2
-  VENDOR
-)
-
 add_entrypoint_object(
   atanh
   SRCS