Fix example gguf_locally to match chat template requirements

[msk]

The gguf_locally example was failing due to a mismatch between the chat template (chat_templates/mistral.json) and the example code. The chat template only supports 'user' and 'assistant' roles, but the example code included a 'system' role message.

When running the example, I encountered the following error:

Error: invalid operation: Conversation roles must alternate user/assistant/user/assistant/... (in chat_template:1)

This PR removes the 'system' role message from the example code to allow it to run successfully.

[github-actions]

Code Metrics Report

  ===============================================================================
 Language            Files        Lines         Code     Comments       Blanks
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 C Header                2           35           28            0            7
 Dockerfile              1           41           22           10            9
 JSON                   12          105          104            0            1
 Python                 63         2706         2339           70          297
 Shell                   1           57           22           18           17
 Plain Text              3         3723            0         2413         1310
 TOML                   18          597          531            2           64
 YAML                    2           21           19            2            0
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 Jupyter Notebooks       4            0            0            0            0
 |- Markdown             2           77           32           31           14
 |- Python               2          205          178            1           26
 (Total)                            282          210           32           40
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 Markdown               43         3312            0         2508          804
 |- BASH                 6          101           98            0            3
 |- JSON                 1           12           12            0            0
 |- Python               7          121          109            0           12
 |- Rust                12          406          344            0           62
 |- TOML                 2           75           63            0           12
 (Total)                           4027          626         2508          893
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 Rust                  283        86228        77444         1776         7008
 |- Markdown           137         1482           25         1349          108
 (Total)                          87710        77469         3125         7116
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 Total                 432        96825        80509         6799         9517
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[EricLBuehler]

Thank you!