BPF: remove duplicate cflags and update btf flags.

With the addition of the -Wall, -Werror, -Wextra cflags to the bpf soong
module as default, they are no longer necessary in the bpf definition in
Android.bp files.

Additionally, 'btf: true'  is now set by default by the build system. To counter this and maintain the existing behavior, add 'btf: false' where necessary.

Test: treehugger
Change-Id: I1961e1ee1cd1e0a83183a79671c66a6af9527f00
Signed-off-by: Neill Kapron <nkapron@google.com>

progs/Android.bp

@@ -30,8 +30,5 @@ cc_library_headers {
 bpf {
     name: "bpfRingbufProg.o",
     srcs: ["bpfRingbufProg.c"],
-    cflags: [
-        "-Wall",
-        "-Werror",
-    ],
+    btf: false,
 }