CLN: remove redundant mac wheel-build code
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

this code is redundant for wheels built using https://github.com/MacPython/pandas-wheels, as the line https://github.com/matthew-brett/multibuild/blob/266d88fe1e474748cc8a3823dc3934bf55e76383/osx_utils.sh#L306 adds tags for 10.9 and 10.10.

Note: circleci fails as I forgot to turn it off on my fork, after it was turned off upstream
great! were you able to build the wheels on a fork to test? yes, although its getting difficult as the mac builds on the wheel builder are starting to hit the travis job timeout (50min) great @robbuckley yeah I think the timeouts are separate (I pushed a fix to see) # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=h1) Report
> Merging [#24644](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d106e9975100cd0f2080d7b1a6111f20fb64f906?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24644/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24644   +/-   ##
=======================================
  Coverage   92.37%   92.37%           
=======================================
  Files         166      166           
  Lines       52379    52379           
=======================================
  Hits        48386    48386           
  Misses       3993     3993
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <ø> (ø)` | :arrow_up: |
| #single | `43.01% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=footer). Last update [d106e99...b390c4c](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=h1) Report
> Merging [#24644](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d106e9975100cd0f2080d7b1a6111f20fb64f906?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24644/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24644   +/-   ##
=======================================
  Coverage   92.37%   92.37%           
=======================================
  Files         166      166           
  Lines       52379    52379           
=======================================
  Hits        48386    48386           
  Misses       3993     3993
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <ø> (ø)` | :arrow_up: |
| #single | `43.01% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=footer). Last update [d106e99...b390c4c](https://codecov.io/gh/pandas-dev/pandas/pull/24644?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @robbuckley  btw I put in place pytest-xdist on the wheels, so finish in about 40 min now :>