Bump to Rust 1.26.2

Remove old versions because they are not compatible with the changes in
rust-common.bbclass

recipes-devtools/rust/rust-llvm_1.26.2.bb

@@ -0,0 +1,16 @@
+require rust-source-${PV}.inc
+require rust-llvm.inc
+
+LIC_FILES_CHKSUM = "file://LICENSE.TXT;md5=e825e017edc35cfd58e26116e5251771"
+
+do_install_prepend () {
+	# the install does a sed on this without installing the file
+	# we don't need it for anything
+	mkdir -p "${D}/usr/share/llvm/cmake"
+	touch "${D}/usr/share/llvm/cmake/LLVMExports-noconfig.cmake"
+}
+
+do_install_append () {
+	# we don't need any of this stuff to build Rust
+	rm -rf "${D}/usr/lib/cmake"
+}