OTA Images: Use esptool.py elf2image --version=2 instead of requiring esptool2

.travis.yml

@@ -5,15 +5,12 @@ env:
   OPENSDK_COMMIT=a48b12f
   CROSS_ROOT="${HOME}/toolchain-${OPENSDK_COMMIT}"
   CROSS_BINDIR="${CROSS_ROOT}/bin"
-  ESPTOOL2_COMMIT=ec0e2c7
-  ESPTOOL2_DIR="${HOME}/esptool2-${ESPTOOL2_COMMIT}"
-  PATH=${PATH}:${CROSS_BINDIR}:${ESPTOOL2_DIR}
   CROSS="ccache xtensa-lx106-elf-"
   MAKE_CMD="make WARNINGS_AS_ERRORS=1 -C examples/ build-examples"
+  PATH=${PATH}:${CROSS_BINDIR}
 cache:
   directories:
     - ${CROSS_ROOT}
-    - ${ESPTOOL2_DIR}
 addons:
   apt:
     packages:
@@ -37,7 +34,6 @@ addons:
     - git
 
 before_install:
-  - utils/travis_build/install_esptool2.sh
   - travis_wait 30 utils/travis_build/install_toolchain.sh
 
 script: