Update uv and remove pip workaround in default image builder

[thomasjpfan]

Why are the changes needed?

With astral-sh/uv#5944 the latest version of uv now works with git & subdirectories.

What changes were proposed in this pull request?

This PR removed the work around with using pip.

How was this patch tested?

I ran this image spec:

from flytekit import ImageSpec, task, workflow

interactive = "git+https://github.com/flyteorg/flytekit.git@master#subdirectory=plugins/flytekit-flyteinteractive"

image = ImageSpec(
    name="interactive",
    builder="default",
    apt_packages=["git"],
    packages=["numpy==1.26.4", interactive],
    registry="localhost:30000",
)


@task(container_image=image)
def fn() -> int:
    import numpy as np

    x = np.array([1, 2, 3])

    return int(x.sum())


@workflow
def main() -> int:
    return fn()

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 43.13%. Comparing base (69445ff) to head (e6f6e78).

Files	Patch %	Lines
flytekit/image_spec/default_builder.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2674       +/-   ##
===========================================
- Coverage   79.24%   43.13%   -36.11%     
===========================================
  Files         196      220       +24     
  Lines       19785    20837     +1052     
  Branches     4008     4005        -3     
===========================================
- Hits        15678     8989     -6689     
- Misses       3407    11620     +8213     
+ Partials      700      228      -472     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.