[examples] fix up examples for new `cargo-contract` with `xbuild` (#320)

* [examples] individual link-args for xargo build

* Add xbuild config to examples

* Run delegator script as nightly

* Enable rlib for flipper

* examples: remove cargo config files

* examples: remove xbuild config

examples/delegator/.cargo/config

-[target.wasm32-unknown-unknown]
-rustflags = [
-	"-C", "link-args=-z stack-size=65536 --import-memory"
-]
\ No newline at end of file

examples/delegator/build-all.sh

 #!/usr/bin/env bash
 
-pushd accumulator && cargo contract build && popd &&
-pushd adder && cargo contract build && popd &&
-pushd subber && cargo contract build && popd &&
-cargo contract build
+pushd accumulator && cargo +nightly contract build && popd &&
+pushd adder && cargo +nightly contract build && popd &&
+pushd subber && cargo +nightly contract build && popd &&
+cargo +nightly contract build

examples/erc20/.cargo/config

-[target.wasm32-unknown-unknown]
-rustflags = [
-	"-C", "link-args=-z stack-size=65536 --import-memory"
-]
\ No newline at end of file

examples/flipper/.cargo/config

-[target.wasm32-unknown-unknown]
-rustflags = [
-	"-C", "link-args=-z stack-size=65536 --import-memory"
-]
\ No newline at end of file

examples/incrementer/.cargo/config

-[target.wasm32-unknown-unknown]
-rustflags = [
-	"-C", "link-args=-z stack-size=65536 --import-memory"
-]
\ No newline at end of file

examples/runtime-storage/.cargo/config

-[target.wasm32-unknown-unknown]
-rustflags = [
-	"-C", "link-args=-z stack-size=65536 --import-memory"
-]
\ No newline at end of file