Remove redundant `mkdir` command in Dockerfiles (#4175)

docker/Dockerfile

@@ -20,7 +20,6 @@ RUN apt update \
 RUN apt upgrade --no-install-recommends -y openssl tar
 
 # Create working directory
-RUN mkdir -p /usr/src/ultralytics
 WORKDIR /usr/src/ultralytics
 
 # Copy contents

docker/Dockerfile-arm64

@@ -15,7 +15,6 @@ RUN apt update \
 # RUN alias python=python3
 
 # Create working directory
-RUN mkdir -p /usr/src/ultralytics
 WORKDIR /usr/src/ultralytics
 
 # Copy contents

docker/Dockerfile-cpu

@@ -15,7 +15,6 @@ RUN apt update \
 # RUN alias python=python3
 
 # Create working directory
-RUN mkdir -p /usr/src/ultralytics
 WORKDIR /usr/src/ultralytics
 
 # Copy contents

docker/Dockerfile-jetson

@@ -15,7 +15,6 @@ RUN apt update \
 # RUN alias python=python3
 
 # Create working directory
-RUN mkdir -p /usr/src/ultralytics
 WORKDIR /usr/src/ultralytics
 
 # Copy contents

docker/Dockerfile-python

@@ -15,7 +15,6 @@ RUN apt update \
 # RUN alias python=python3
 
 # Create working directory
-RUN mkdir -p /usr/src/ultralytics
 WORKDIR /usr/src/ultralytics
 
 # Copy contents