[C31][UBOOT] remove already-existing patch
Remove patch 0006-Add-target-to-generate-initial-environment.patch, which was already committed to branch next of u-boot-seco-rk Commit: cbca032016b0cfad1527abbe05c3696c32834ba5
This fixes a bitbake error when trying to modify u-boot-seco-rk (C31) with devtool