Pkg.rm removes [targets] from Project.toml

[sostock]

Removing any package from a project via Pkg.rm removes the [targets] section from the Project.toml:

julia> versioninfo()
Julia Version 1.0.3
Commit 099e826241 (2018-12-18 01:34 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i7-3520M CPU @ 2.90GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, ivybridge)

(v1.0) pkg> generate Foo
Generating project Foo:
    Foo/Project.toml
    Foo/src/Foo.jl

(v1.0) pkg> activate Foo

julia> f = open("Foo/Project.toml", "a"); write(f,
       """

       [extras]
       Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

       [targets]
       test = ["Test"]
       """); close(f);

shell> cat Foo/Project.toml
authors = ["<removed>"]
name = "Foo"
uuid = "2e060878-13ed-11e9-0e15-0759cb5991b0"
version = "0.1.0"

[deps]

[extras]
Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

[targets]
test = ["Test"]

(Foo) pkg> add Unicode
  Updating registry at `~/.julia/registries/General`
  Updating git-repo `https://github.com/JuliaRegistries/General.git`
 Resolving package versions...
  Updating `~/Downloads/julia-1.0.3/bin/Foo/Project.toml`
  [4ec0a83e] + Unicode 
  Updating `~/Downloads/julia-1.0.3/bin/Foo/Manifest.toml`
  [4ec0a83e] + Unicode 

shell> cat Foo/Project.toml
name = "Foo"
uuid = "2e060878-13ed-11e9-0e15-0759cb5991b0"
authors = ["<removed>"]
version = "0.1.0"

[deps]
Unicode = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"

[extras]
Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

[targets]
test = ["Test"]

(Foo) pkg> rm Unicode
  Updating `~/Downloads/julia-1.0.3/bin/Foo/Project.toml`
  [4ec0a83e] - Unicode 
  Updating `~/Downloads/julia-1.0.3/bin/Foo/Manifest.toml`
  [4ec0a83e] - Unicode 

shell> cat Foo/Project.toml
name = "Foo"
uuid = "2e060878-13ed-11e9-0e15-0759cb5991b0"
authors = ["<removed>"]
version = "0.1.0"

[extras]
Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

[fredrikekre]

duplicate of #876