gallium/tools/trace: use python shebang

Currently the upstream guidance is that if a script works with both
python2 and python3 to use python as the shebang. This also remove
shebangs from non-executable files.
35 jobs for !8367 with wip/2020-12/trace-tools-py3 in 9 seconds (queued for 3 seconds)
latest detached
Status Job ID Name Coverage
  Sanity
passed #6519007
sanity

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  Container
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aarch64 manual
arm_build
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arm_test-base
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windows shell 1809 mesa manual
windows_build_vs2019
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manual
x86_build-base
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manual
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android_build
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armhf_test
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kernel+rootfs_amd64
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aarch64
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aarch64
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ppc64el_build
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s390x_build
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x86_build
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x86_test-gl
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x86_test-vk
 
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meson-clang
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meson-clover
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meson-gallium
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meson-release
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meson-testing
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meson-testing-asan
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meson-vulkan
 
  Build Misc
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meson-android
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aarch64
meson-arm64
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aarch64
meson-arm64-build-test
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aarch64
meson-armhf
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meson-i386
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meson-mingw32-x86_64
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meson-ppc64el
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meson-s390x
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allowed to fail
scons-win64